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We'll take it ingredient by ingredient and step by step through Heidi's recipe. Here it is so you can follow along:

• Mushroom Casserole from Heidi Swanson of 101 Cookbooks

Let's start with the veggies:

The Mushrooms - If we're going to make a mushroom casserole, we have to have mushrooms! We like to use brown mushrooms like Heidi mentions in her recipe, but you can definitely use white, shiitake, portabella, or any other mushrooms you like. Different mushrooms will give the casserole different flavors and textures.

We like to leave the mushrooms in fairly large chunks, which gives the casserole a chunkier texture and a satisfying chewiness. If you chop them more finely - which you can certainly do! - the mushrooms will melt into the other vegetables. Instead of bursts of mushrooms, you'll get a nice background mushroom flavor throughout the casserole.

After they're chopped, Heidi tells us to cook them until they've released their liquid and browned a bit. This is starting to build the flavor in the dish. As the mushrooms cook, their surfaces start to turn golden-brown and caramelize thanks to the Maillard Reaction. The liquid being released has a lot of flavor that will then get mixed with the other ingredients. You can also let the liquid simmer and reduce to further concentrate the flavor.

The Onions - Cooked onions lose their sharp flavor and become savory sweet. If you want even more of this flavor, let the onions cook with the mushrooms until they go beyond translucent and start to turn golden.

The Garlic - You only want to cook the garlic until you can start to smell it, 30-60 seconds. This is just enough time to infuse the dish with garlic flavor, but much more and it will start to burn. This is why it gets added after the mushrooms and onions have already finished cooking.

All these veggies make up the main flavor base for the casserole. You can also add any spices that you're in the mood for, like thyme, oregano, rosemary, or even chili and cumin for a Southwestern twist! We've also added cooked chicken, sausage, or bacon when we have any leftover in the fridge.

The Rice - Heidi's recipe uses cooked brown rice, but she assures us that we can use any grain we like. And we have! Each kind of grain has its own particular flavor and texture, so changing it up is an easy way to add some variation to this recipe. Our favorites are pearl barley, israeli cous cous, or wild rice (as in the photo above).

The veggies and rice are the body of the casserole. Everything else works to bind it together.

The Eggs - The eggs are the main binder. As they cook, their proteins form a network that sets the liquid and makes the casserole firm. The thinly the eggs are spread once they're mixed with all the other ingredients, the less they will be able to set. If you like a gooier casserole, try taking out an egg or using one egg and one egg yolk. If you like a more firm casserole, try adding another egg or an egg white.

The Cottage Cheese and the Sour Cream - The cottage cheese and sour cream also help to set the casserole, but they mostly add richness and flavor. If you're out of one of these two ingredients, you could try substituting another dairy like yogurt, creme fraiche, or even a little cream cheese. Aim for the same consistency as the cream cheese-sour cream mix and it should work!

The Parmesan - Parmesan adds a great savory, nuttiness to this dish. We also like using pecorino, feta, and ricotta salata.

The whole casserole gets baked at a fairly low temperature so that the proteins in the eggs and dairy have a chance to set slowly. If the oven is too hot, the resulting casserole could end up rubbery and dry. Covering the casserole with aluminum foil at the beginning of cooking also helps to regulate the temperature and keep the top from drying out.

And that's it! We haven't had a bad experience with this casserole yet. With the layers of flavor and the creaminess from the dairy, it really hits the spot.

What additional ingredients or variations could you see making with this recipe?

Related: Baking Lab: Why Did Our Cake Fall Flat?

(Image: Emma Christensen for the Kitchn)