Set a large skillet over medium heat, add the olive oil, sausage, diced onion, kosher salt, pepper, and crushed red pepper flakes. Cook 7 to 9 minutes, stirring a few times and breaking the sausage apart with a spatula.

Sprinkle some of the flour, stir until combined. Add a little more flour and stir. Then add the rest of the flour and stir for another 2 to 3 minutes.

Add the milk, and more kosher salt, pepper, crushed red pepper flakes and bring to a boil. Once boiling, reduce the heat to low and stir occasionally for about 10 to 12 minutes. Stir in the cheese during the last minute until melted.

Grease a 9 x 13 casserole dish or 10 to 12 inch cast iron skillet. Cut each biscuit into fourths and arrange them around the casserole dish or cast iron skillet, overlapping so they all fit. Bake in a 375 degree oven for 8 to 9 minutes.

Pour the sausage gravy in the center (be careful as the pan will be hot) and bake in a 375 degree oven 11 to 13 more minutes.

Let cool slightly before serving and garnish with chives if desired.