In a large bowl, whisk together flour, baking powder, salt, sugar, black pepper, and red pepper. Using a pastry blender or 2 forks, cut in cold butter until mixture is crumbly. Add cheeses and 3⁄4 cup buttermilk, stirring until a thick dough forms. Add remaining ¼ cup buttermilk, if needed.
On a lightly floured surface, gently knead dough 4 or 5 times. Roll or pat dough into an 8-inch square; cut into 25 pieces. Place dough pieces close together in a 10-inch square cast-iron skillet.
Bake until golden brown, about 17 minutes. Let cool for 15 minutes.
Using a large spatula, remove from pan and cut into pieces. Brush with melted butter. Serve with mustard and ham.
Recipe by Southern Cast Iron at https://southerncastiron.com/cheese-pepper-biscuits/