Place the 3 lb Yukon Gold potatoes peeled and cut into 1½-inch chunks chunks in a large pot and cover with cold water by at least 1 inch. Add a generous pinch of kosher salt (about 1 tbsp). Starting in cold water ensures the potatoes cook evenly all the way through.

Bring the pot to a boil over high heat, then reduce to a steady simmer. Cook the 3 lb Yukon Gold potatoes peeled and cut into 1½-inch chunks until completely tender — a fork or knife should slide in and out with zero resistance, about 18–22 minutes. Don't rush this step; undercooked potatoes make lumpy mash.

While the 3 lb Yukon Gold potatoes peeled and cut into 1½-inch chunks cook, warm the ¾ cup heavy cream and ¼ cup whole milk together in a small saucepan over low heat, or microwave in a heatproof cup for about 60 seconds until steaming. Keep warm. Cold dairy added to potatoes will make them gluey and dense.

Drain the 3 lb Yukon Gold potatoes peeled and cut into 1½-inch chunks thoroughly in a colander and return them to the hot pot over low heat. Shake the pot gently for 1–2 minutes to evaporate any remaining moisture — this is key for fluffy, non-watery mash.

Pass the 3 lb Yukon Gold potatoes peeled and cut into 1½-inch chunks through a ricer or food processor directly back into the pot for the silkiest result. Alternatively, use a potato masher for a more rustic, slightly textured mash. Avoid using a hand mixer or blender — overworking the starch makes potatoes gluey.

Add the room-temperature 8 tbsp unsalted butter cut into tablespoon pats pats a few at a time, folding them in gently with a spatula or wooden spoon after each addition. Let each addition melt fully before adding the next. Adding butter before the cream gives you a richer, more emulsified result.

Pour in the warm ¾ cup heavy cream and ¼ cup whole milk mixture gradually, folding it in until the 3 lb Yukon Gold potatoes peeled and cut into 1½-inch chunks reach your desired consistency. You may not need all of it, or you may want a splash more ¼ cup whole milk for a looser mash — adjust to your preference.

Season with 1½ teaspoons of kosher salt and the ¼ tsp white pepper freshly ground. Taste and adjust — potatoes need more salt than you think. Fold gently to combine.

Transfer to a warm serving mixing bowl. Make a shallow well in the center and pour in the optional melted unsalted butter cut into tablespoon pats. Garnish with fresh fresh chives thinly sliced if desired. Serve immediately.