Preheat the oven to 375°F (190°C). Lightly grease a muffin tin with butter.
In a large bowl, mix the mashed potatoes, shredded cheese, eggs, sour cream, green onions, garlic powder, salt, and black pepper until well combined.
Stir in the baking powder and flour until the mixture is smooth and thick.
Spoon the mixture into the prepared muffin tin, filling each cup about three-quarters full.
Bake for 25-30 minutes, or until the puffs are golden brown and crispy on the edges.
Let cool for a few minutes before serving. Enjoy warm!