Combine the shallots, wine lemons, salt, and white and black peppers in a saucepan over high heat. Bring to a boil, mashing the lemons with the top end of a whisk. Stir in the dill and cook for 3 minutes.
Whisk in the mustard and cream and cook, stirring occasionally, for 2 minutes. Whisk in the butter a few pats at a time, turn off the heat, and continue whisking until the butter is thoroughly incorporated. Strain the sauce through a fine sieve, pressing all the liquid through with the back of a spoon. Serve immediately or prepare except for the butter. Store the sauce, refrigerated, in an airtight container for up to 24 hours. Reheat in a saucepan over low heat, and when the sauce comes to a simmer, whisk in the butter and proceed from there.
Yield: 3/4 cup