In a 10- to 12-inch frying pan, combine 1 cup fat-skimmed chicken broth and 1 cup dry white wine. Boil over high heat until reduced to about 2/3 cup, about 10 minutes.
Add 2 teaspoons Dijon mustard and 6 tablespoons unsalted butter in a chunk and whisk until butter is blended into boiling sauce. Continue to boil and stir until sauce is reduced to about 2/3 cup and thick enough to coat a spoon in a velvety layer, 3 to 5 minutes. Add lemon juice to taste. Use hot.