There are so many ways to make soups or soup like things that we need to narrow in first on our target soup.
In this case, we are looking for vegetable heavy, brothy soups. So not stews or purées.
More specifically, soups that have the propensity to make their second coming a luxurious experience. Something that both your doctor and toilet manufacturer would be proud of (read: full of fiber).
These soups are slightly more viscous than water, full of solids that are cut small enough that at least a few can fit on a spoon, but each solid is identifiable.
In the order in which they are generally cooked:
Let's dig into each one:
Fat is useful for flavor, chemical extraction, and heat distribution. Starting with flavor, we are all wired to seek calories. In modern life, this is arguably not useful anymore. I can easily find way more calories than I need, and that can become an issue. But that also means that our palates love fat. And I don't mean eating straight fat, though good olive oil and butter sure are nice straight. When fat has been properly integrated (many times emulsified) into something, it just tastes way better. But for this section for soup, we are not really after too much of that here.
Fat extracts chemicals, as we will see in a later section. Many of the chemicals that provide "spice" or "heat" are fat soluble. Read on to that section.
A base fat is most useful for heat transfer. Fat has a great property of being both slick and slippery, but also sticky and coating. Kind of a strange juxtaposition of properties. Put a pan on your burner and turn it on. You now have a single direction of heat flow - heat leaves the pan. But a pan is a cooking volume, not just a surface. It has 3 dimensions (4 when you think about how long you are applying the heat...) so the depth of the food needs to be taken into account.
I guarantee that if you dice up onion and sauté it in a dry pan vs a pan with some fat, the onions are going to be unevenly cooked in the dry pan. The pan will scorch one side of each onion piece, and not touch the other side, resulting in half raw, half burnt onions.
Fat conducts heat a lot better than air or water, which are usually the only other mediums that heat has a chance to travel through in your pan (excluding the pan itself) to get to the food. By coating the food in fat, the heat from the bottom of the onion piece (where it touches the pan) can better travel around to the top, into the upper volume of the pan, and cook the onion evenly.
That movement of heat via the fat evenly cooks the onion and evens out the temperature. Now the heat in the pan is being used to heat a much larger volume than it was when dry. This is why fat is so important to begin with.
What do we put into that base fat? We put aromatics. French cuisine has their mirepoix - onion, carrot, celery - Cajun cuisine has the holy trinity - onion, celery, green bell pepper - and there are many more. Most cuisines have a typical set of base vegetables that they start with. It helps a cuisine retain familiarity, and is usually a set of vegetables that are easy to grow in the region.
Focussing on mirepoix (or soffritto for Italian cuisine) as that is what I usually put in these soups. Alliums really are an impressive culinary vegetable. They have a complex set of flavors that really compliment almost anything else. The common alliums include onions, garlic, shallots, and leeks. Carrots have a lot of sugars in them as well. Celery adds bitterness that helps to quell the sweetness from the others and allow their more subtle flavors to shine.
Cooking down the base aromatics first is pretty important. We need to get the moisture out of them to concentrate their flavor. We also want to rupture their cell(?) walls to get those sugars into the pan and give them a good dose of the Maillard reaction. That is the serious muscle behind flavor building.
The degree to which these aromatics are cooked initially depends on what your goal is - what flavors are you hoping for them to express. The less cooked they are the more piquant and vegetal they will be, the more you cook them (slower and longer) the more caramelized, mellowed, and deepened their flavors will become.
Seasoning check in! It's time to add salt to build flavor and help break down those cell(?) walls.
There should be more to your soup than just base aromatics. The additional solids can be split into groups based on where they sit between hearty and delicate. Super generally, you can say that the lower to the ground, and in fact if they are buried, the item is, the heartier it will be. Root vegetables are hearty, and leaves are delicate. But obviously that is not always correct - peppers can be very robust and they sit in the leaf area. Collard greens require the same type of cooking as tough cut of meat even.
Another way to look at it is to have 3 groups - things that need to be sautéed, things that need to be simmered, and things that need to be wilted. For this soup, that means that bell pepper and zucchini should be sautéed, parsnips and turnips should be simmered, and kale should be wilted (if not simmered a bit too).
The other notable solids are mushrooms. These must be sautéed. Owing to their social ineptitude, I usually start these first. They don't even like being by each other in a pan, let alone other aromatics. Without crowding them, mushrooms will relax and release way more liquid than seems possible. Once this has cooked away, you are left with some very mushroom-y mushrooms, which is exactly what you want.
Seasoning check in! It's time to add salt to build flavor and help break down those cell(?) walls.
I like putting in my tough fresh herbs at this point. Rosemary, thyme, sage, and things along those lines. I keep them whole on the branch(?) and tie them together in a bouquet garni. Which is one way of saying just tie the sprigs together with kitchen twine so that you can fish them out later.
I want to say I know something about how the herbs interact with the sugars and fats we have built up in the pan and release more flavor, but I'd be lying. Its a working theory that I can't be bothered to actually look up. If nothing else it helps transform the smell, and that alone is worth it. Only put these in for a few min tops before you add the liquid.
I don't know all of them, but many things we call spices are fat soluble. So we want to add them when there is fat in the pan to extract their flavors, and not much water to hider that. Anything with capsaicin fits in here, as well as most warm spices, black pepper, and I want to say some green herbs like oregano.
Just add them and stir for a minute or less.
When adding things like oregano or other green dried herbs, here's a tip. Put it into your left palm, right in the center where you can cup your palm. Then take your right hand and fit the bottom of the palm, right before the heel, into that area. It should look like you have two hands, palms pushed against each other, but the right hand is an inch or so up so that its past the bottom of your thumb. Then twist them back and forth to grind the green herbs into a powder. This will release a lot of that goodness locked in the herbs.
I grew up reading recipes that asked for garlic to be the first thing in, before sautéing the other aromatics. I still have not been able to reconcile that recommendation with any experience that I've had. I feel like it was a period of pretty poor recipe writing. Garlic is so prone to burning, it should be added last unless you are very carefully planning on cooking it for an extended period of time at lower heat and know what you are doing.
The first liquid in the pan should always be alcohol. Brewing and distillation (extend that to fermentation) are purposefully designed to extract flavor. That flavor can then go into our soup. Wine is common, liquors are great for getting some complex flavors in, and beer gives you those malty bread-y vibes that work well too. Pick something that you enjoy drinking with this kind of food, or from the same region that your flavors are from.
A good sub for this is vinegar or liquid from fermented items.
Water is a good start but it dilutes. Sometimes that is all you want - you want the flavors that you just built up to be exactly what the soup tastes like. Other times, and in this case, you want to use a liquid that brings something to the party. How about some chicken stock - the blank canvas of the kitchen. Check out the other post about making this yourself. Its worth it for soups like this.
This is optional, as is I guess everything else here. But in this case of a minestrone type soup, it's going to be tomatoes. I usually have some spare tomato sauce type liquid, or canned tomatoes in my kitchen. They add a great depth of flavor, acid, and sweetness that is appreciated.
Now bring it to a boil, drop it to a simmer, and cover it.
Seasoning check in! Water nor homemade chicken stock will have salt in it, so you need more salt. It can be jarring seeing how much salt soup needs. Its a lot of mass though, and that mass needs salt.
The soup should simmer until it's read for the landing sequence. That includes things that you don't want to overcook. Everything in the pot up until now can essentially be cooked indefinitely. But we have other things we want to add that can be. Think parsnips or potatoes. They may need ~30 min of cooking but if you give then 2 hours they will be mush and fall apart.
This is also the time to add any grains or pasta. For those, as well as anything here, you can pre cook them outside the soup and then add them. This is beneficial as they will not suck up all the tasty broth you have made, but on the flip side they will have absorbed water, which makes them taste less interesting. So sometimes I will water down my broth before adding these items, in the hopes they will help balance it back out to the right flavor concentration, while also being flavored.
Alternatively just make the soup way broth-y-er than it needs to be and these items will help balance that without losing any flavor.
Kale, chard, spinach - leaves that need to be cooked and can stand some serious heat, but really don't need too much.
At this point the soup is pretty much done. Taste for seasoning and adjust 3 things - fresh cracked black pepper, salt, and acid. The 3 of those things will help the soup pop in different ways. Taste and adjust for each one. You will probably need acid at least at this stage.
Have you ever been to a fancy restaurant where they bring you soup, and its actually a dry bowl with a beautiful arrangement of perfectly cooked ingredients, and then they pour a soup from a pitcher into the bowl? I've always found that to be a fun experience. Especially when they have things like croutons or other ingredients that will change when the soup hits them.
In my case, I have found that thinly sliced cabbage is an awesome addition to the bottom of a soup bowl. Also delicate herbs like parsley or cilantro. The heat of the soup poured over them will begin to wilt them, but you will still get crunch. I love it. The idea for cabbage comes from eating pozole - a favorite soup of mine that is many times finished with raw cabbage.
Things that you don't want to be cooked - good olive oil, fresh cracked black pepper, lemon, and cheese.
Soup is always better the next day.
If you have something like a grain or pasta in your soup, it will make it its life mission to absorb as much broth as possible. That means that tomorrow and the next day, your soup will progressively look more like pasta salad than soup. Which is why, if you plan on having leftovers and eating them for lunch, its good to also make extra stock that you can use to water down the soup on subsequent days.