In 3-quart saucepan, melt butter over medium heat. Cook onion and garlic in butter, stirring frequently, until tender. Sprinkle flour over onion mixture; cook 1 minute, stirring constantly. Gradually add half-and-half, stirring constantly until thickened and bubbly. Stir in salt, cumin and pepper. Add cheese and chipotle chiles; stir until cheese is melted. Pour cheese sauce over potatoes.