Scrub the red potatoes thoroughly under running water to remove dirt. Leave the skins on. Trim any dark spots or sprouts and cut larger potatoes into 1½–2 inch pieces so all pieces are similar size for even cooking.

Optional garlic (softened)

If using garlic, add the peeled whole cloves to the pot with the potatoes so they will soften and mellow during boiling.

Start cold water and salt

Place the cut potatoes (and garlic, if using) in a large pot. Pour in cold water until potatoes are covered by about 1 inch. Add kosher salt (about 1 tablespoon). Starting with cold water helps potatoes cook evenly.

Boil and simmer

Bring the pot to a boil over high heat, uncovered. Once boiling, reduce heat to maintain a gentle rolling boil and cook until a fork or paring knife slides easily into the largest pieces, about 12–18 minutes depending on size. Do not overcook until falling apart.

Drain and steam dry

Drain the potatoes and garlic in a colander. Return the drained potatoes to the hot pot and set the pot over the still-warm burner (turned off) for 1–2 minutes to let excess surface moisture evaporate. This prevents watery mashed potatoes.

Warm dairy and melt butter

While the potatoes steam-dry, warm the milk and half-and-half with the butter in a small saucepan over low heat until the butter melts and the mixture is hot but not boiling (or microwave in a heatproof container for 45–60 seconds). Warming the dairy keeps the potatoes hot and absorbs better.

Mash

Use a potato masher or ricer to mash the potatoes and softened garlic directly in the pot until you reach your desired texture. For chunkier red-skin mashed potatoes leave some small potato pieces and skins intact; for smoother results use a ricer and then fold.

Add dairy and season

Gradually pour the warm butter-milk mixture into the mashed potatoes, stirring gently with a wooden spoon or rubber spatula until incorporated and creamy. You may not need all the liquid—add until you reach your preferred consistency. Taste and add salt (start with 1 teaspoon) and freshly ground black pepper (about 1 teaspoon), adjusting to taste.

Finish and serve

Transfer the mashed potatoes to a serving bowl, dot with a little extra butter if desired, and sprinkle sliced chives over the top. Serve hot.