Place the peeled and quartered potatoes in a large pot and cover with cold water. Add 1 teaspoon salt.
Bring to a boil over high heat. Reduce the heat to medium-low and simmer for 15–20 minutes, or until the potatoes are fork-tender.
Drain the potatoes well and return them to the pot.
Add the butter to the hot potatoes and mash with a potato masher until mostly smooth.
Meanwhile, combine the milk, heavy cream, and minced garlic in a small saucepan. Warm over low heat until heated through. Do not boil.
Gradually add the warm milk mixture to the potatoes, mashing until smooth and creamy.
Stir in the remaining 1 teaspoon salt and black pepper.
Serve warm.
Notes
For extra rich potatoes, you can increase the amount of butter or use all heavy cream instead of a mix of milk and cream.Refrigerate the leftovers in an airtight container for up to 5 days.