From Chateau Chantal
1/4 cup water
1/4 cup sugar
3 T. red-wine vinegar
1 cup finely chopped onion (about 1 medium)
3 T. unsalted butter
2 cups Chateau Chantal Trio
2 cups rich veal stock
In a small heavy saucepan bring water with sugar to boil, stirring until sugar is dissolved. Boil syrup, without stirring, until a golden caramel. Remove pan from heat and carefully add vinegar down side of pan (caramel will steam and harden). Cook caramel over moderate heat, stirring, until dissolved, about 3 minutes, and remove pan from heat.
In a heavy saucepan cook onion in butter over moderate heat, stirring, until golden, about 5 minutes. Stir in wine and boil until mixture is reduced to about 1 cup, about 15 minutes. Stir in stock and boil until mixture is reduced to about 2 cups, about 10 minutes. Remove pan from heat and stir in caramel. Pour sauce through a sieve into a bowl.
Sauce may be made 2 days ahead, cooled completely, and chilled, covered. Reheat sauce before serving.