This cheesy, golden, puffed casserole is all about the eggs

By America’S Test Kitchen The Associated Press

Despite its name, this “omelet” is nothing like the filling-stuffed egg dish you expect at brunch, nor does it take a day to bake. This cheesy, golden, puffed casserole is all about the eggs, consisting of a rich custard, bread, and cheese and yielding a melt-in-your-mouth texture that rivals even the fluffiest scrambled eggs.
The eggs should be this dish’s focus, not the bread, so to keep their flavour at the fore, we prepared a milk-based custard. Buttered white bread, cut into bite-size pieces and layered with tangy cheddar cheese in a baking dish, promised to melt right into the custard while also bringing in plenty of richness.
A small amount of grated onion and a bit of dry mustard and hot sauce added just enough complexity to the creamy eggs. Refrigerating the assembled omelet overnight melded the flavours and saturated the bread, so all we had to do before brunch was bake it.
Cheesy and golden, this humble casserole puffed impressively above the rim of the baking dish, making it a tempting but unfussy centerpiece. Use the large holes of a box grater to grate the onion.
The omelet needs to sit in the refrigerator, well covered, for at least 8 hours in order to achieve the desired consistency.
Servings: 6-8
Start to finish: 1 hour 30 minutes (plus 8 hours chilling time)
3 tablespoons unsalted butter, softened
10 slices hearty white sandwich bread
12 ounces cheddar cheese, shredded (3 cups)
8 large eggs
3 cups whole milk
1 small onion, grated
1 teaspoon salt
1/2 teaspoon pepper
1 teaspoon dry mustard
1/2 teaspoon hot sauce
Grease 13-by-9-inch baking dish. Spread butter evenly over 1 side of bread slices, then cut into 1 inch pieces. Scatter half of bread evenly in prepared dish and sprinkle with half of cheddar. Repeat with remaining bread and cheese.
Whisk eggs, milk, onion, salt, pepper, mustard, and hot sauce together in bowl until well combined. Pour egg mixture evenly over bread and press lightly on bread to submerge. Wrap dish tightly with plastic wrap and refrigerate for at least 8 hours.
Adjust oven rack to middle position and heat oven to 350 F. Unwrap casserole and bake until puffed and golden, about 1 hour. Serve immediately.
Variations:24 hour “omelet” with sun-dried tomatoes and mozzarella: Substitute mozzarella cheese for cheddar. Add 1/2 cup grated Parmesan cheese and 1/2 cup oil-packed sun-dried tomatoes, patted dry and chopped, between 2 layers of bread in step 1. Sprinkle 3 tablespoons minced fresh cilantro over top before serving.
24 hour “omelet” with pepper jack and chipotle chile: Substitute pepper Jack cheese for cheddar and 2 to 3 teaspoons minced canned chipotle chile in adobo sauce for dry mustard and hot sauce. Sprinkle 3 tablespoons minced fresh cilantro over top before serving.