In a 12-inch cast-iron skillet, heat oil over medium-high heat. Add sausage; cook until browned and crumbly, about 6 minutes. Stir in flour; cook, stirring constantly, for 1 minute. Gradually whisk in milk, thyme, salt, and pepper until smooth. Remove from heat. Place Buttermilk Biscuits on top of gravy.
In a small bowl, whisk together egg and 1 teaspoon water; brush onto biscuits.
Bake until biscuits are golden brown and gravy is bubbly, 20 to 22 minutes. Let stand for 5 minutes. Garnish with thyme, if desired.
Buttermilk Biscuits
Line a baking sheet with parchment paper.
In a large bowl, cut cold butter into flour using a pastry blender until mixture is crumbly. Stir in cold buttermilk with a fork just until combined.
Turn out dough onto a heavily floured surface, and knead several times until dough comes together. Pat or roll dough to ¾-inch thickness.
Using a 2-inch round cutter dipped in flour, cut dough without twisting cutter; reroll scraps as necessary. Place 2 inches apart on prepared pan. Freeze for at least 15 minutes or while making gravy.
Notes
Unbaked biscuits can be frozen in a heavy-duty resealable plastic bag for up to 3 months. Want buttermilk biscuits without the gravy? Place frozen biscuits on a parchment-lined baking sheet, brush with egg wash, and bake at 425° for 15 to 18 minutes.
Recipe by Southern Cast Iron at https://southerncastiron.com/buttermilk-biscuit-sausage-gravy-cobbler/