1/2poundshiitake mushroomsstems discarded and caps cut into 3/4-inch pieces
1medium onionminced
1red bell peppercut into 1/2-inch pieces
2teaspoonskosher saltplus more for seasoning
8large eggs
3cupswhole milk
1tablespoonspicy mustard
1tablespoonlow sodium soy sauce
1/2teaspoonpepper
3/4poundday-old challahsliced 1 inch thick and cut into 1-inch dice (10 cups)
1cupshredded Monterey Jack cheese1/4 pound
1cupshredded aged white cheddar cheese1/4 pound
1/2cupfinely chopped scallionsplus thinly sliced scallions for garnish
Hot saucefor serving
Instructions
Butter a large 9 x 13 inch baking dish and set off to the side.
Heat olive oil in a large skillet. Add the pepperoni and bacon. Cook until just about crisp. Add mushrooms, onion, and bell pepper. Cook until tender. Remove from heat and allow to cool while you get the remaining ingredients together.
In a large mixing bowl, whisk together the salt, eggs, milk, mustard, soy sauce, and pepper. Add the challah to the mixture. Allow to soak for a minute or two. Next, mix in both cheeses and the scallions. Pour the mixture into the baking dish. Cover with plastic wrap and place in the refrigerator. Let the casserole soak overnight.
In the morning, preheat the oven to 350 degrees F. Uncover the casserole and bake for 50-60 minutes until the top is golden brown and the center is no longer jiggly. If you notice the top is browning too quickly, cover with tin foil and continue to bake. Allow the casserole to cool for at least ten minutes before serving.