There Is Only One Secret to Perfect Green Bean Casserole
My mother is particular about many things, but perhaps nothing more than her belief that homemade cream of mushroom soup is the single most important ingredient in a truly great green bean casserole. This belief is deeply held by her, partially because she is from Indiana (which I guess makes her an expert on casseroles) and partially because her mother, my grandmother, was a somewhat erratic cook who made some things very well, and other things very… oddly.
As far as I can tell, one of the things my grandmother made very, very well was a green bean casserole, largely because she was a sort of functional hippie who used very few processed foods in her cooking. This meant, of course, that she would never use canned cream of mushroom soup. My mother, who is also a functional hippie has carried on this tradition, and makes a stellar green bean casserole every year. And every year, we make a fuss about how important it is that she make the condensed "soup" from scratch.
As little as I want to admit that my mom is right about literally anything, she is correct about the soup. Canned cream of mushroom soup has too little mushroom flavor, and too many preservatives. Texturally, it can get very weird when baked in a casserole. When you make this element from-scratch, it gives the casserole a backbone that you just can't fake.
GET THE RECIPE: Best Green Bean Casserole
If you're annoyed that I just gave you a whole new step, know that you can make the soup quite far in advance and freeze it. If you do this, say, a few weeks before Thanksgiving, it offers the ease of using canned soup, so don't stress.
The most important step in making your cream of mushroom soup is making sure that you deeply caramelize the mushrooms. This means cooking them undisturbed in a hot pan for at least five minutes, with plenty of oil and no salt. The no-salt part is key, because mushrooms hold a lot of water, and salting them too early in the cooking process will release that water, which inhibits their ability to get all crispy and caramelized. Crispy and caramelized is where the flavor lives. If you're patient and loving with your mushrooms, you'll make a soup that is unlike anything you've had from a can, possibly leaving you doubting whether you should put it in the casserole at all.
I will say this: I deviate from my mother and grandmother's rules in one place: I use pre-made fried onions. I believe them to be the superior option, and I've found that when homemaking crispy onion topping, it is nearly impossible to make enough because you're actually just making onion rings and everyone around you (and also you) will just want to eat them. It's not worth the work or the conflict with your family, so I use store-bought. I have to rebel against my mother somehow.