Melt the butter in a small sauce pan over high heat. Add shallot and cook 2 minutes. Add the wine and bring to a boil. Boil until it is reduced to about ½ cup. This may take 5-10 minutes depending on the size of your saucepan.
Reduce heat to medium and add the cream, sugar and salt. Stir to mix and then add the lemon juice and mustard. Simmer until it thickens enough to coat the back of your spoon. Adjust seasoning to taste.
Allow the sauce to cool about 10 minutes. It will continue to thicken as it cools.
Serve warm over seafood or vegetables and rice as desired.