In a medium saucepan, melt butter over medium heat, and then stir in flour. Cook until flour is brown (1 2 min). Stir in milk until flour mixture dissolves. Continue to cook, stirring constantly until sauce thickens. Add rest of ingredients and continue to stir until fully mixed. Do not bring to a boil.
Pour over cooked chicken or cooked asparagus. Leftover sauce needs to be refrigerated in an airtight container. For reuse, heat up sauce in a saucepan on medium heat for approximately 3 5 minutes, stirring occasionally.