Warm stock in a heavy-based saucepan over medium heat.

Melt butter in another pan. Stir in flour and cook about 3 minutes or so until bubbly. Gradually ass warmed stock, whisking constantly. Cook, uncovered, at a slow simmer for about 50 minutes to one hour, stirring occasionally, until reduced by one-third.

Skim any foam that may have arisen to the top during cooking. Strain through cheesecloth or a fine sieve. Keep hot in a top double boiler until ready to use. Adjust seasoning to taste.

Serve over broiled chicken or lightly cooked vegetables.