Melt the butter in a pan and stir in the flour to make a roux. Cook gently for 1 minute. Remove the pan from the heat, and gradually stir in the stock and wine. Finally, add the cream, tarragon and a little salt and pepper to taste. Return to the heat and simmer gently for 10 minutes, then stir in the cheese and the mustard. Taste and adjust seasonings.
Serve with roast chicken, or use in a chicken gratin as above.
© 1990 Joyce Molyneux. All rights reserved.