In a large skillet over medium heat, cook the breakfast sausage, breaking it up into small pieces as it cooks. Add the dried minced onion to the skillet and continue cooking until the sausage is well browned and no longer pink. Drain any excess fat if necessary.

Crack the eggs into a large mixing bowl and whisk until smooth. Add the whole milk, salt, and ground black pepper, and whisk again until everything is well combined. I like to take my time whisking here to ensure the mixture is light and fluffy.

Preheat your oven to 350°F (175°C). Grease a casserole dish with butter or nonstick spray. Add 3/4 of the cooked sausage with onion (from Step 1) to the bottom of the dish. Top this layer with half of the shredded sharp cheddar cheese.

Pour the egg mixture (from Step 2) evenly over the sausage and cheese layers in the casserole dish. Place the casserole into the preheated oven and bake for 30 minutes, or until the eggs are mostly set in the center.

After 30 minutes of baking, remove the casserole from the oven. Sprinkle the remaining shredded sharp cheddar cheese and the reserved cooked sausage with onion (from Step 1) over the top. Return the casserole to the oven and bake for another 10-15 minutes, until the cheese is well melted and the center is completely set. For a nice golden top, you can broil it for an extra minute or two—I always think this makes the dish look even more appetizing!

Allow the casserole to cool for a few minutes before slicing it into squares for serving. Enjoy your delicious breakfast!