Butter a 9x13 inch baking dish and set aside.
In a large skillet cook the pork sausage and diced onion over medium heat until the sausage has browned.
16 ounces ground pork sausage, 1 small yellow onion
Reduce the heat to medium-low and sprinkle the flour over the sausage. Stir to combine.
3 Tablespoons all-purpose flour
Slowly add in the 2 ½ cups (591 mL) whole milk, about ¼ cup at a time, stirring well after each addition.
2 ½ cups whole milk
When all of the milk has been added stir in the black pepper, garlic powder, and salt. Continue to cook, stirring occasionally, until warmed through and thickened, about 5 minutes. Remove the gravy from the heat.
1 teaspoon ground black pepper, ¼ teaspoon garlic powder, ¼ teaspoon fine sea salt
Preheat the oven to 350° F. Cut the biscuits into pieces and spread them out in the prepared baking dish.
16.3 ounces refrigerated biscuits
In a large mixing bowl, whisk together the eggs, ½ cup (118 mL) milk, garlic powder, onion powder, salt, and black pepper until well-combined. Pour the mixture over the biscuit pieces.
6 large eggs, ½ cup milk, ½ teaspoon garlic powder, ½ teaspoon onion powder, ¼ teaspoon fine sea salt, ¼ teaspoon ground black pepper
Sprinkle the cheese evenly over the eggs and biscuits and pour the sausage gravy on top.
1 cup white cheddar cheese
Bake for 35-40 minutes or until the casserole is cooked through.