Preheat the oven to 350°F (175°C).
Peel and chop the potatoes into even-sized pieces.
Boil the potatoes in a large pot of salted water until tender, about 15-20 minutes.
Drain the potatoes and return them to the pot.
Add butter, sour cream, milk, garlic powder, salt, and pepper to the pot with the potatoes.
Mash the potatoes using a potato masher until smooth.
Stir in the cheddar cheese until melted and evenly distributed.
Transfer the mixture to a greased baking dish.
Bake in the preheated oven for 30-35 minutes until golden on top.
Let cool for a few minutes before serving.