Wash the Yukon Gold potatoes thoroughly under cold water, cut into even cubes, and place in a large pot covered with cold water.

Add 1 tablespoon of kosher salt and bring to a boil, then simmer for 15-20 minutes until fork-tender.

In a separate saucepan, heat the heavy cream and butter over medium heat, then add garlic cloves and rosemary.

Let it steep for 10 minutes, stirring occasionally to prevent scorching.

Drain the potatoes and return them to the warm pot; mash until smooth and creamy.

Gradually fold in the warm cream mixture into the mashed potatoes, and season with kosher salt and black pepper to taste.

Transfer to a serving dish, garnish with rosemary and butter if desired, then serve warm.