Preheat oven to 450°F. Line a baking sheet with parchment paper or lightly grease a cast-iron skillet.
In a large bowl, combine homemade biscuit mix, garlic powder, and onion powder (if using).
Stir in shredded cheddar cheese until evenly distributed.
Pour in cold buttermilk and gently stir just until a soft, slightly sticky dough forms. Do not overmix.
Using a scoop or spoon, drop dough into evenly sized mounds onto the prepared pan or skillet.
Bake for 10–12 minutes, or until biscuits are golden and cooked through.
Remove from oven and immediately brush tops with melted butter. Serve warm.