Combine first 3 ingredients in a medium saucepan; heat on low and whisk until smooth. Stir in 1/2 cup Swiss cheese; heat and whisk until smooth. Do not boil. Season sauce to taste with salt and pepper. Combine cheese sauce and hot pasta; spread mixture into a greased 8 x 8 baking pan. Top with remaining cheese. Place pan under broiler until cheese melts and is lightly browned, 5-7 minutes. Makes 6-8 servings.