Preheat Oven: Set to 220°C and line a baking sheet with parchment paper.
Mix Dry Ingredients: Combine flour, sugar, baking powder, and salt in a large bowl.
Incorporate Butter: Grate or cube cold butter and cut it into the flour using a pastry cutter or fingers until the mixture resembles coarse crumbs.
Add Wet Ingredients: In a separate bowl, whisk sour cream, egg, and vanilla. Pour into the dry mixture and gently combine until a shaggy dough forms. Fold in any optional mix-ins.
Shape Dough: Lightly flour a surface, turn out the dough, and gently pat into a disk.
Chill Dough: Refrigerate for 20-30 minutes to allow the flour to hydrate and firm up the butter.
Cut and Prepare: Cut into wedges or use a biscuit cutter. Place on the baking sheet with 2 inches between each. Brush tops with milk or cream and sprinkle sugar if desired.
Bake: Bake for 16-20 minutes until golden brown. Cool lightly on a wire rack before serving.
