Melt butter in a small saucepan over medium-low heat; add garlic, and sauté until tender. Remove from saucepan, and set aside.
Prepare mashed potatoes in saucepan according to package directions, using 2 1/3 cups milk and stirring with a wire whisk.
Stir in garlic mixture, salt, and pepper. Let potatoes stand 5 minutes before serving.