Place potatoes and garlic cloves in a large saucepan; cover with water. Bring to a boil. Reduce heat; cover and cook for 15-20 minutes or until potatoes are tender. , Meanwhile, in a small saucepan, heat butter and cream; keep warm. Drain potatoes and garlic; return to pan. Add the horseradish, salt, pepper and butter mixture; mash to reach desired consistency. Garnish with thyme if desired.