Preheat the Oven:
Preheat your oven to 375°F (190°C). Grease the baking dish.
Prepare the Sausage Gravy:
In a large skillet, cook the sausage over medium heat until browned, breaking it up into crumbles. Drain excess fat.
Stir in the flour and cook for 1-2 minutes to form a roux.
Gradually whisk in the milk, cooking and stirring until the mixture thickens and becomes gravy. Season with salt, pepper, and sage if using.
Prepare the Biscuits:
Cut each biscuit into quarters and place them in the bottom of the greased baking dish.
Assemble the Casserole:
Pour the sausage gravy evenly over the biscuit pieces in the baking dish.
Sprinkle 1/2 cup of shredded cheddar cheese over the top.
Bake:
Bake in the preheated oven for 20-25 minutes, or until the biscuits are cooked through and the top is golden brown.
If using, sprinkle an additional 1/4 cup of shredded cheddar cheese on top during the last 5 minutes of baking.