Open the oysters as instructed in previous recipe ("Opening Oysters in the Microwave"). Measure 1/2 cup of the strained cooking liquid and reserve.
Melt the butter in a 1-quart glass or ceramic measure or bowl, uncovered, on high for 2 minutes. Stir in 1/2 cup reserved oyster juices and Champagne and cook, uncovered, on high, stirring twice during cooking, for 4 minutes or until thickened. Recipe can be made to this point a few hours ahead.
COOKING AND SERVING:
Heat the broiler with rack set at its highest level. Stir celery seed and white pepper to taste into the sauce. Spread 2 cups of coarse or rock salt in the bottom of a broiler pan to steady oysters.
Nestle reserved shells into salt. Put each oyster in a shell and thoroughly coat the tops with sauce. Put under preheated broiler until just golden, about 2 minutes.
Makes 4 first-course servings.
NOTE: This is a simple and elegant classic. You can prepare the oysters and sauce ahead in the microwave, and then broil for a minute or two just before serving. The obvious wine to serve is Champagne. If you choose another dry sparkling wine to drink instead, use the same one in the sauce.