Boil wine, vinegar, and shallot in a 2- to 3-quart heavy saucepan over moderate heat until liquid is syrupy and reduced to 2 to 3 tablespoons, about 5 minutes. Add cream, salt, and white pepper and boil 1 minute. Reduce heat to moderately low and add a few tablespoons butter, whisking constantly. Add remaining butter a few pieces at a time, whisking constantly and adding new pieces before previous ones have completely liquefied (the sauce should maintain consistency of hollandaise), lifting pan from heat occasionally to cool mixture. Remove from heat, then season to taste with salt and pepper and pour sauce through a medium-mesh sieve into a sauceboat, pressing on and then discarding shallot. Serve immediately.