In a medium bowl, combine self-rising flour and butter. Grate butter into flour, or add cold cubes, and cut in using a snapping motion with your fingers until crumbly (can also use a fork or pastry cutter.)

Add buttermilk and mix until just combined. Do not overmix.

Turn dough out onto a floured surface. Gently fold two or three times and then press or roll out to about ½ inch tall rectangle.

Cut biscuits, put on a sheet pan, and place in the freezer for 15 minutes while you prepare the rest of the casserole components.

Preheat oven to 375°F. Grease the inside of a square pan or casserole dish with butter and/or non-stick spray.

Heat a non-stick pan, or other skillet, over medium-high heat and add one tablespoon of vegetable oil. Add your potatoes and season to taste with salt and pepper. Cook, stirring occasionally, for 8 to 9 minutes, or until potatoes are fully cooked and lightly browned. Place them in the bottom of your prepared pan

Place the pan back on the heat and cook your breakfast sausage, breaking it up with a spatula or wooden spoon. Cook until all the pink color is gone and the sausage is browned, about 8 to 10 minutes. Scatter the sausage on top of the potatoes.

Whisk your eggs. Place the pan back on the stove and decrease heat to medium. Cook your eggs until soft scrambled. You want them to still look a bit undercooked as they will continue to cook in the oven. Scatter the eggs on top of the sausage.

In the same pan, over medium-high heat, melt your butter and sprinkle flour over it. Whisk them together and cook for about a minute. Continue whisking while you pour in half of the milk. Whisk vigorously to be sure there are no lumps.

Remove biscuits from freezer and cut into quarters and scatter over the casserole components, leaving space between them. For golden color, brush tops of biscuits with an egg wash (an egg whisked with 1 tablespoon of water) or more buttermilk.