Lightly spray a 10-inch cast-iron skillet with cooking spray. Line a large rimmed baking sheet with parchment paper.
In a large bowl, cut butter into flour using a pastry blender until mixture is crumbly; stir in 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 2¼-inch round cutter dipped in flour, cut dough without twisting cutter; place biscuits on prepared baking sheet. Reroll scraps and cut as necessary. Freeze biscuits for at least 15 minutes.
Preheat oven to 425°.
Place biscuits in prepared skillet. In a small bowl, whisk together egg and 1 teaspoon water; brush onto biscuits. Sprinkle with seasoning.
Bake until golden brown, 20 to 25 minutes. Let cool in pan on wire rack for 5 to 10 minutes. Serve warm with cream cheese.
Notes
To bake biscuits later, freeze cut biscuits for 12 hours in step 3. Transfer biscuits to a heavy-duty resealable plastic bag, and freeze for up to 3 months. Bake as directed, increasing time by 5 minutes.
Recipe by Southern Cast Iron at https://www.southerncastiron.com/everything-buttermilk-biscuits/