Wash, peel, and chop the yellow potatoes into 1" pieces.
Peel and smash three garlic cloves. Mince the other two garlic cloves and set aside.
Place the chopped potatoes and garlic cloves in a deep pot. Fill the pot with enough cold water to cover the potatoes by one inch. Sprinkle in a heavy pinch of kosher salt, and bring the pot to a boil.
Boil the potatoes for 6-8 minutes until a fork can easily pierce one of the potato cubes. Turn off the heat from under the pot and drain the water.
Add butter and minced garlic to the potatoes. Use a potato masher to mash the potatoes with the butter and garlic.
Stir in milk and sour cream until smooth.
Stir in cheese until melted. Season with extra salt and pepper to taste.