Preheat oven to 400º. Place potatoes in a large pot and cover with two inches of water. Season with salt.
Bring to a boil and boil until tender, 15 minutes. Drain until cool enough to handle.
Transfer potatoes to a baking sheet. Pour over melted butter, garlic, and season with salt and pepper. Toss until totally combined.
Using the bottom of a small glass or jar, smash potatoes into flat patties.
Bake until crispy, 20 to 25 minutes more.
Top with cheddar and bake until melted, 3 minutes more.
Top with cooked bacon, green onions, and sour cream (if using) and serve.
