1. Melt butter in a heavy saucepan over low heat; add shallots and garlic, and sauté 1 minute. Whisk in flour until smooth. Cook 1 minute, whisking constantly.
2. Increase heat to medium. Gradually whisk in milk; cook over medium heat, whisking constantly, 5 to 7 minutes or until mixture is thickened and bubbly. Stir in salt, pepper, and nutmeg.
Note: Mixture can be made ahead and stored in an airtight container in the refrigerator up to two days. Warm sauce over low heat before using.