1 tbsp. butter
1 tbsp. all-purpose flour
1 c. milk
2 tbsp. prepared mustard
1/2 tsp. salt

Melt butter, stir in flour. Cook until smooth, stirring constantly. Remove from heat. Gradually stir in milk. Add mustard and salt. Bring to a boil, stirring constantly. Boil and stir 1 minute. Serve over hot cooked asparagus spears.