Place the potatoes into a large saucepan and add enough water to cover them, plus about 1 inch. Cook over medium-low heat until fork tender, about 15 to 20 minutes.
In a medium saucepan, melt butter, add half and half and garlic. Heat until simmering.
Drain potatoes and pour them back into the saucepan used for cooking. Mash over low heat until smooth.
Add the melted butter and half and half mixture to the potatoes. Continue to mash until creamy. Stir in horseradish, salt, and pepper until light and fluffy.
Pour potatoes into a serving bowl and serve warm.
