Preheat your oven to 375°F (190°C) and grease a muffin tin or line it with muffin liners.
In a large mixing bowl, combine the mashed potatoes, cheddar cheese, Parmesan cheese, eggs, milk, green onions, garlic powder, onion powder, salt, and pepper. Mix until everything is well combined and creamy.
Scoop the potato mixture into the prepared muffin tin, filling each cup to about three-quarters full.
In a small bowl, mix the breadcrumbs with melted butter, then sprinkle generously over the top of each muffin for a crunchy topping.
Bake in the preheated oven for about 25-30 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean.
Once baked, remove from the oven and let them cool in the pan for 5 minutes before transferring to a wire rack to cool completely, or enjoy warm.
Notes
Serve warm with sour cream or a dip for added flavor.