2 cups milk
12 large eggs
2 teaspoons dry mustard
2 teaspoons salt
1 teaspoon black or white pepper
1 loaf French bread, crust trimmed, cut into 1-inch pieces (leave out several hours to dry out)
1 pkg mushrooms, diced and sautéed
1 each green and red bell pepper, diced and sautéed
1 medium onion, diced and sautéed

1 cup (packed) grated sharp cheddar cheese

Sauté mushrooms with one tablespoon butter or margarine.  Set aside to cool.  Repeat with the bell peppers and then with the onion.  There's no need to rinse out the pan between vegetables. 

Beat milk, eggs, and mustard in large bowl to blend.  Mix in bread, cheese, and cooled vegetables.  Transfer mixture to 13x9 glass dish. Cover with foil and chill overnight.

Preheat oven to 375°F. Bake strata uncovered until just set in center, about 60 minutes. (Cover with foil after 40 minutes if browning too quickly.) Remove foil and sprinkle additional cheese over top.  Bake until cheese melts, about 10 minutes longer. Let stand 10 minutes and serve.