Begin by peeling (if desired) and cutting Yukon Gold potatoes into 1-inch cubes. Place in a large pot and cover with cold water. Add 1 tablespoon kosher salt. Bring to a boil, then reduce to a simmer. Cook for 15-20 minutes, or until fork-tender.

In a small saucepan, combine unsalted butter and heavy cream over medium heat. Stir until melted and hot, not boiling. Add garlic cloves and rosemary. Steep for 10 minutes to infuse flavors.

Once the potatoes are tender, drain and return to the pot. Mash to desired consistency. Gradually incorporate the cream mixture until thoroughly combined and creamy.

Taste and adjust seasoning with salt and pepper. Give a final stir and serve hot, garnished with rosemary or a pat of butter.