Place butter in a 1 1/2 quart casserole. Microwave on high (100%) until melted, 30 seconds to 1 minute. Stir in next four ingredients. Blend in half and half, milk and sherry. Microwave on medium-high (70%) until thickened, 4 to 7 minutes, stirring with wire whisk two or three time during cooking. Stir small amount of hot mixture into egg yolks; return to mixture. Microwave at medium-high (70%) until thickened, 1 to 3 minutes, stirring once or twice. Stir in crab meat. Serve over toast points or patty shells, if desired.