Prepare Oven: Preheat oven to 425°F (220°C). Line a standard baking sheet with parchment paper.
Combine Dry Ingredients: In a large mixing bowl, whisk together the flour, baking powder, sugar, salt, and garlic powder until well combined.
Cut in Butter: Add the cubed cold butter to the dry ingredients. Using a pastry blender or two forks, cut the butter into the flour mixture until it resembles coarse crumbs.
Add Onion and Cheese: Stir in the finely chopped onion and the shredded cheddar cheese, if using, distributing them evenly.
Form Dough: Pour in the milk or buttermilk. Mix gently with a spoon or spatula until a soft, shaggy dough forms. Be careful not to overmix.
Drop Biscuits: Drop generous spoonfuls of dough (approximately 2 tablespoons each) onto the prepared baking sheet, leaving about 1 inch of space between each biscuit.
Bake: Bake for 12 to 15 minutes, or until the biscuits are golden brown on top and cooked through.
Brush with Butter: While the biscuits are baking, melt the 2 tablespoons of butter in a small bowl. Immediately upon removing the hot biscuits from the oven, brush them generously with the melted butter.
Serve: Serve warm.
