Preheat your oven to 375°F (190°C). Lightly grease a 9-inch pie plate or a deep baking dish to prevent sticking.
In a large pan set over medium heat, cook the sausage until browned thoroughly and crumbled, about 6 to 8 minutes. Drain any residual grease and set the meat aside.
Using the same skillet, add the butter and melt it fully. Stir in the flour and cook for 1 minute, stirring continuously to form a smooth roux.
Gradually pour in the milk, whisking constantly to prevent lumps. Cook for 5 to 7 minutes, until the sauce thickens to a creamy consistency.
Incorporate the garlic powder, onion powder, black pepper, salt, and optional red pepper flakes into the gravy. Mix the cooked sausage back in and take the skillet off the heat.
Open the biscuit can and separate each biscuit. Cut each one into four equal parts.
Arrange half of the biscuit quarters in an even layer at the base of your prepared dish.
Pour the sausage gravy mixture over the biscuit layer. If using eggs, whisk them thoroughly and drizzle evenly over the gravy before adding cheese.
Sprinkle the shredded cheddar over the filling.
Finish by arranging the remaining biscuit quarters on top in a loose lattice or scattered pattern.
Place in the oven uncovered and bake for 25 to 30 minutes, or until the biscuits are golden and baked through. If they brown too quickly, tent loosely with aluminum foil during the final 10 minutes.
Allow the pie to sit for 5 minutes before slicing.
Top with fresh parsley just before serving for added color and flavor.