Small Sauces: Robert

Cook 4 oz (120 g) chopped onion in butter without browning. Add 1 cup (240 mL) white wine and reduce by two-thirds. Add 1 qt (960 mL) demi-glace and simmer 10 minutes. Strain and add 2 tsp (10 mL) dry mustard and a pinch of sugar dissolved in a little lemon juice.