Preheat oven to 350°F. Grease a 9x13 inch baking dish with cooking spray and set aside.

Cook the ground breakfast sausage in a large skillet over medium-high heat, breaking it up with a wooden spoon as it cooks. Cook for 8-10 minutes until browned and no pink remains.

Drain the cooked sausage completely using a slotted spoon. Remove as much grease as possible—this is crucial for a non-greasy casserole. Set the drained sausage aside to cool slightly.

In a large mixing bowl, crack the eggs and add the whole milk. Whisk vigorously until completely combined and slightly frothy. Season with salt, black pepper, garlic powder, and onion powder. Whisk again until seasonings are fully incorporated.

Spread the frozen hash browns in an even layer on the bottom of your greased baking dish. You can use thawed hash browns, but frozen works fine.

Sprinkle 1 cup of the shredded cheddar cheese evenly over the hash brown layer.

Add the cooked and drained sausage in an even layer over the cheese.

Pour the whisked egg mixture slowly and evenly over all the layers, making sure it reaches every corner of the pan.

Top with the remaining 1 cup of shredded cheddar cheese, spreading it evenly over the entire surface.

Bake uncovered in the preheated 350°F oven for 45-50 minutes, until the center is completely set and a knife inserted in the middle comes out clean. The eggs should be puffed and no longer jiggly.

Remove from oven and let the casserole rest on the counter for 10 minutes before cutting. This allows the eggs to set properly for clean slices.

Cut into 8 squares and serve hot. Garnish with fresh herbs, salsa, or hot sauce if desired.