Bring 5 cups of water to boil, then add the potatoes and ¼ teaspoon salt; boil the potatoes for 15 minutes.
After 15 minutes, drain the boiled potatoes and let it cool for a while.
Transfer the potatoes into a mixer, then mix until crushed.
After crushing all the potatoes, transfer it into a pan, add the garlic, butter, heavy cream, mozzarella cheese, and ground black pepper. Mix well over low heat.
When the mixture is already thickened, transfer it into a bowl.
Serve hot and enjoy!