This is a truly easy cheese sauce. It’s best served immediately—over baked potatoes, broccoli or polenta.
1. Place flour in heavy medium saucepan, and gradually whisk in milk, then mustard, until blended. Cook over medium heat, stirring constantly, about 8 minutes, or until thickened.
2. Remove from heat. Add cheeses, stirring until melted. Season to taste with salt and pepper. Serve warm.