Grease a 2-quart straight-sided saute pan with the butter. Add the Champagne, shallots, dill sprigs, chopped dill, and salt and pepper and bring to a boil. Reduce the heat to medium-low. Gently simmer for 5 minutes.

Add the fish to the pan and spoon the poaching liquid over them. Cook uncovered until the salmon is firm and cooked through, about 10 minutes. (If the poaching liquid does not cover the fish, spoon the liquid over the fillets as they cook.)

Using a slotted spatula, remove the fillets from the pan and blot excess liquid with a paper towel. Serve with the Champagne-Vanilla Sauce.

In a saucepan, combine the shallots and Champagne. Scrape the vanilla seeds from the split pod into the pan and add the vanilla pod halves. Bring to a boil and cook until almost all liquid evaporates, about 6 minutes.

Add the heavy cream, bring to a boil and simmer until cream thickens and coats the back of a spoon, and is reduced by nearly 50 percent in volume, about 3 minutes.

Whisk in the butter until smooth and strain the sauce through a fine mesh strainer, pressing on the solids to extract as much liquid as possible. Season, to taste, with salt, pepper, and vinegar and serve immediately over fish or shellfish.

Note: If sauce is made in advance, keep warm in a bain marie over barely simmering water.

Yield: About 1 generous cup, 4 servings