Brown 1 pound ground breakfast sausage in frying pan. Drain well and set aside.
Generously coat inside of slow cooker with no-stick cooking spray (or wipe down with vegetable oil).
Add 8 eggs to a medium mixing bowl and whisk lightly.
Add cooked sausage and 1 1/2 cups shredded cheddar cheese to eggs in bowl, then stir to combine.
Pour egg mixture into prepared slow cooker and season generously with salt and pepper.
Use kitchen scissors (or a paring knife) to cut 1 (8 ounce) tube refrigerated buttermilk biscuit doughinto bite-size pieces. Arrange biscuit pieces evenly on top of egg mixture in slow cooker.
Cover slow cooker with lid and cook on high for 2 hours (or low for 4 hours) or until egg mixture is set and biscuit pieces are cooked through.
To Prepare Sausage Gravy:
Heat 2 (15 ounce) cans sausage gravy according to package directions.
To Make Homemade Gravy (optional):
Melt ¼ cup salted butter in saucepan over low-medium heat.
Add ¼ cup all purpose flour to saucepan, and whisk while cooking over low-medium heat until slightly golden brown.
Add 2 cups milk, 1 teaspoon salt, and 1 1/2 teaspoons ground black pepperto the saucepan, and stir over medium-high heat until it comes to a boil.
Reduce heat to low-medium and simmer until thickened to desired consistency.
To Serve Biscuits & Gravy Casserole:
Top individual servings of casserole with warm gravy before serving.