Prep the potatoes: Cut the red potatoes into even chunks, about 1.5 to 2 inches. Keep the skins on for color and texture. Rinse once to remove surface starch.
Start in cold water: Place potatoes in a large pot and cover with cold water by about 1 inch. Add 1 tablespoon kosher salt and the smashed garlic if using.
Boil until tender: Bring to a steady boil, then reduce to a lively simmer. Cook 12–15 minutes, until a fork slides in easily with no resistance.
Warm the dairy: In a small saucepan over low heat, melt butter with the cream. Keep it warm—warm dairy blends better and prevents gummy potatoes.
Drain and steam-dry: Reserve 1/2 cup of the cooking water, then drain potatoes well. Return them to the hot pot and let them sit 1–2 minutes to steam off excess moisture.
Mash gently: Use a potato masher for a rustic texture or a ricer for ultra-smooth. Avoid a food processor or blender. Mash about 75% of the way.
Add butter and cream: Pour in about two-thirds of the warm butter-cream mixture. Add sour cream, salt, and pepper. Mash and fold until creamy.
Adjust texture: Add more warm cream as needed. If you want silkier potatoes, stir in a splash of the reserved starchy water to loosen while keeping them glossy.
Taste and finish: Adjust salt and pepper. Add an extra pat of butter on top for shine. Sprinkle with chives or parsley.
Serve warm: Transfer to a warm bowl and enjoy immediately for the best texture.
