Fill the pot with enough cold water to cover. Add a big pinch of salt to the water. This seasons the potatoes from the inside out.

Place the pot on the stove over high heat. Bring the water to a full rolling boil. Let the potatoes cook for fifteen to twenty minutes.

Test the potatoes with a sharp fork or knife. They should be tender but not falling apart yet. Drain them well using a large kitchen colander.

Preheat your oven to 450 degrees Fahrenheit now. Line your baking sheet with a piece of parchment. Let the potatoes dry for a few minutes.

Place the potatoes on the prepared baking sheet. Use your masher to press down on each one. They should be about half an inch thick.

Drizzle the melted butter and olive oil over them. Sprinkle the salt, pepper, and garlic on top. Make sure every potato is well coated with oil.

Slide the baking sheet into the hot oven now. Roast them for twenty to twenty-five minutes total. They should look golden brown and very crispy.