This is an easy go-to, adaptable, make ahead meal. Use any greens or alliums you have, use a lot or a little. Use up any bits of cheese or meat or vegetables you have in the refrigerator, anything you have will be delicious.
I had some onions, spinach and mushrooms leftover from some pizza I made earlier so I used up those leftovers. I made this in a loaf pan. You can easily double this and bake it in a 9 X13 pan.
Spinach and Onion Strata
I used about 2 cups total vegetables
1/2 teaspoon salt
a few cranks of fresh black pepper
4 cups cubed bread
about a cup of cheese
1 1/4 cups milk
4 or 5 eggs
1 tablespoon Dijon mustard
You will want any vegetables you use in your strata cooked and cooled before you assemble the dish, so do that first.
Next spread one third of the bread cubes in a well-buttered oven proof dish. Top with one-third of your vegetable mixture and one-third of the cheese. Repeat layering twice with remaining bread, spinach and cheese.
Whisk eggs, milk, mustard and remaining 1/2 teaspoon salt and 1/4 teaspoon pepper together in a large bowl and pour evenly over strata. Cover with plastic wrap and chill strata for eat least 8 hours or up to a day. All that egg and milk need to get soaked up in the bread.
Preheating the oven to 350°F. Bake strata, uncovered, in middle of oven until puffed, golden brown, and cooked through, 45 to 55 minutes. Let stand 5 minutes before serving.