Place the potatoes and garlic cloves in a large pot. Fill the pot with water until it covers the potatoes by 2". Cover, and heat over medium high heat until the water comes to a boil. Remove the lid, reduce the heat to medium, and simmer until the potatoes are tender, about 15 minutes.

Preheat the oven to 350 degrees F. Drain the potatoes well in a colander then place back in the empty pot. Mash the potatoes with a potato masher or ricer until they reach the desired consistency.

Add 1/2 cup of the cheese, sour cream, milk, butter, rosemary, salt and pepper and stir until well to combine. Add more milk as desired, then taste and adjust the seasoning, if necessary.

Grease a 9×13" baking dish with cooking spray and add the potatoes. Top with the remaining cheese and bake until warmed through and the cheese has melted, about 30 minutes. Serve immediately and enjoy!