Preheat the oven to 450°F. In a large bowl, whisk the flour, baking powder, sugar, salt and cream of tartar. Cut the butter into the dry ingredients until the mixture resembles coarse crumbs. Editor's Tip: If you don't have (or don't want to use) a pastry blender, you can use a food processor to mix the dry ingredients, scatter in cubes of cold butter and briefly pulse.
Stir in the cheddar, garlic and pepper flakes. Add the milk and stir just until moistened. Editor's Tip: A good biscuit tip is not to overmix the dough. When you add the milk, stir until it all just comes together. No kneading necessary.
Drop dough by heaping ¼ cupfuls, 2 inches apart on a greased or parchment-lined baking sheet. Bake for 18 to 20 minutes or until golden brown. Serve warm. Editor's tip: Not all ovens are created equal. If yours has hot spots, rotate the pan halfway through the cooking time. You could also cook these at 425° to reduce the risk of singeing the biscuit bottoms.
