1. Melt butter in a heavy saucepan over low heat; whisk in flour until smooth. Cook 1 minute, whisking constantly. Gradually whisk in milk; cook over medium heat, whisking constantly, until mixture is thickened and bubbly. Whisk in Swiss and Parmesan cheeses, salt, and red pepper, whisking until cheeses are melted and sauce is smooth.
Go to Full Version of