Make-Ahead Vegetarian Breakfast Casserole

By Carolyn Gratzer Cope¹⁾

This wonderfully savory make-ahead vegetarian breakfast casserole is brimming with vegetables. It’s perfect to feed a crowd on Christmas morning or at a festive brunch. I like to use my 5-quart braiser for this dish, because it can go from stovetop to oven. If you don’t have one of those, you can do the stovetop part in a 12-inch skillet and the baking part in any 5-quart baking dish.

Le Creuset Signature Enameled Cast-Iron 5-Quart Round Braiser, Cerise (Cherry Red)

▢4 tablespoons (56 grams) butter
▢1 medium yellow onion, diced small
▢1 green bell pepper, diced small
▢1 red bell pepper, diced small
▢10 ounces (283 grams) sliced shiitakes
▢1 teaspoon fine sea salt, divided
▢10 ounces (283 grams) frozen chopped broccoli or small florets, defrosted
▢10 large eggs
▢3 cups (710 ml) whole milk
▢¼ teaspoon freshly ground black pepper
▢⅛ teaspoon ground nutmeg
▢⅛ teaspoon ground cayenne
▢8 cups (400 grams) unseasoned dry stuffing cubes/bread cubes
▢5 ounces (142 grams) shredded gruyere, divided
▢¼ cup (30 grams) grated parmesan or pecorino, divided

• Melt the butter in the braiser or skillet over medium-high heat.
• Add the onion, green pepper, red pepper, and shiitakes all at once, along with 1/2 teaspoon of the salt.
• Cook, stirring from time to time, for about 10 minutes, until the vegetables have softened, browned a bit, and decreased in volume by at least half.
• Remove from heat.
• While the other vegetables cook, place the defrosted broccoli on a thick layer of paper towels and cover with another thick layer.
• When the veggies in the skillet have cooked as noted above, press down gently on the paper towels to remove moisture from the broccoli. Alternatively, cook the broccoli briefly in the microwave and drain well.
• Add broccoli to the skillet and stir to incorporate.
• Crack the eggs into a large mixing bowl and beat well with a fork.
• Stir in milk, remaining salt, pepper, nutmeg, and cayenne.
• Add bread cubes and stir to moisten evenly.
• Stir in all the vegetables, half the gruyere and half the parmesan or pecorino.
• Grease the braiser or baking pan with a little bit of butter or cooking spray and pour the whole mixture in. Sprinkle with the remaining cheese.
• Let rest for at least 30 minutes — up to 24 hours — so that the bread cubes have a chance to completely absorb the liquid. If resting for more than about an hour, Cover and refrigerate.
• An hour before serving time, preheat oven to 375°F with a rack in the center and remove casserole from fridge.
• Bake uncovered for about 40 minutes, until puffed and golden. Serve hot or even at room temperature.

I use whole milk to make the casserole just rich enough, but you can substitute anything from half-and-half to low-fat milk if you prefer. Use a really good-quality butter if you can. Here and virtually everywhere, I start with a cultured, salted butter from grass-fed cows. This sounds fancy but doesn't have to be. Kerrygold, for example, is sold in most supermarkets at a reasonable price. I've called for a good old yellow onion, which works very well. You can substitute an equal quantity (about one cup total, chopped) of shallot, leek, or red onion if you prefer. A combo of green bell pepper and red bell pepper contributes a nice balance of flavors plus a festive pop of color. But you can use any color(s) that you like. Shiitakes are boldly flavored and low in moisture, both of which I love for this recipe. You can substitute a different variety of mushroom if you prefer. Just be sure to cook off all the excess moisture before adding to the egg mixture. The recipe calls for frozen chopped broccoli, which I like because it distributes easily throughout the casserole. That said, I am finding it nearly impossible to source these days. Petite broccoli florets will work just fine, too. Either way, you'll choose between defrosting them and blotting well between paper towels, or briefly cooking them in the microwave and draining well before stirring into the mix. Gruyere instantly elevates a recipe with its umami-forward, nutty, slightly funky flavor. If it's important to you that this dish be vegetarian, be sure to choose a brand made without animal rennet. If you'd rather, you can substitute another semi-hard cheese that melts well, like cheddar, provolone, fontina, or Swiss. Choose a good-quality, freshly grated parmesan cheese. It gets stirred into the egg mixture and also sprinkled on top, and it adds a ton of savoriness to this dish. If it's important to you that this dish be vegetarian, be sure to choose a brand made without animal rennet. It's important to prep the casserole at least 30 minutes before putting it into the oven, so that the bread cubes have a chance to fully absorb the liquids. You can prepare the whole thing up to about 24 hours in advance, cover it, and pop it into the fridge before baking. Bake straight from the fridge, adding a few minutes to the cooking time, or let it rest on the counter for about an hour before baking. If you're cooking for a smaller group, feel free to halve the recipe. When I do this (as you can see in the video, if you look carefully), I actually like to leave the quantities of the vegetables, cheeses, and spices intact and halve the rest of the ingredients (butter, eggs, milk, bread cubes, and salt and pepper). You can halve everything if you prefer. Leftovers will keep in an airtight container in the fridge for a week and can be reheated in the microwave, or in a covered pan in the oven or toaster oven.