I made this for my family last Easter and it was devoured. It is easy to assemble and tastes great. A real family pleaser.
Cook the bacon in a large, deep skillet over medium-high heat until evenly browned, about 10 minutes. Drain the bacon slices on a paper towel-lined plate. Crumble the bacon and set aside.
Place a steamer insert into a saucepan and fill with water to just below the bottom of the steamer. Cover and bring the water to a boil. Add the asparagus, cover, and steam until bright green but still crunchy, about 5 minutes. Remove asparagus and set aside.
In a large bowl, whisk together eggs, milk, dry mustard, salt, and pepper until smooth and well combined.
Grease a 9x13-inch baking dish. Layer the bread slices into the bottom of the dish, cutting and fitting extra slices as needed to fill spaces. Sprinkle 1 cup of Cheddar cheese over the bread, followed by the diced onion. Arrange asparagus spears and red bell pepper in a layer over the onion. Sprinkle crumbled bacon over the red bell pepper; top with another layer of bread slices, cutting and filling in spaces as before. Pour the egg-milk mixture evenly over the casserole, and refrigerate overnight.
Preheat oven to 350 degrees F (175 degrees C).
Bake the casserole for 50 minutes; sprinkle 1 cup shredded Cheddar cheese over the top of the casserole, return to the oven, and bake until the cheese is melted and bubbling and a knife inserted into the center of the casserole comes out clean, 10 to 15 more minutes.
Per Serving: 483 calories; protein 28g; carbohydrates 35.7g; fat 25.3g; cholesterol 240mg; sodium 1312.6mg.