How to Make It
Place butter in a small saucepan over medium-low heat; cook until butter melts, stirring occasionally. Add onion to pan; cook 10 minutes or until tender (do not brown), stirring occasionally. Sprinkle flour over onion; cook 2 minutes, stirring occasionally.
Gradually add milk to flour mixture, stirring with a whisk until smooth; bring to a simmer. Simmer 10 minutes or until thickened, stirring frequently. Strain mixture through a fine sieve over a bowl; discard solids.
Stir in salt, pepper, and nutmeg, if desired. Serve immediately.
Mornay Sauce: Prepare Béchamel Sauce. Wipe pan clean with paper towels. Return Béchamel Sauce to pan, and place over medium-low heat. Add 1/2 cup (2 ounces) shredded Gruyère cheese, stirring until smooth. Serve immediately. Yield: 1 1/2 cups (serving size: about 2 1/2 tablespoons).
Calories 67; Fat 2g (sat 1g, mono 4g, poly 3g); Protein 9g; Carb 3g; Fiber 0g; Chol 16mg; Iron 1mg; Sodium 92mg; Calc 97mg