1 Melt butter in a heavy, large saucepan over medium-low heat.
2 Whisk in flour until golden, about 1 minute. Gradually whisk in milk. Bring to boil; cook and whisk for 2 minutes or until thickened.
3 Reduce heat to low; gradually stir in swiss and parmesan until melted. Remove from the heat. Season with salt and pepper to taste.