In a large bowl, place flour. Using a pastry blender or 2 forks, cut in butter until mixture is crumbly. Gradually add buttermilk, stirring just until dry ingredients are moistened.
On a lightly floured surface, gently knead dough 4 times. Roll dough about ¾ inch thick. Fold dough in half. Using a 3-inch round cutter, cut dough, rerolling scraps once.
Wipe bottom and sides of an 8- to 10-inch cast-iron skillet with oil. Place pan in oven until very hot, about 5 minutes. Place biscuits in hot pan, overlapping slightly if needed.
Bake until golden brown, about 15 minutes. Let cool in pan for 5 minutes
Recipe by Southern Cast Iron at https://southerncastiron.com/buttermilk-biscuits/