Preheat oven to 350°F. Brush bread with melted butter and use cookie cutter to cut
about 40 moons out of bread slices. Arrange, buttered sides up, on a large baking
sheet and bake in middle of oven until pale golden, about 10 minutes. Cool completely.
Serve toasts topped with sour cream and caviar.
Cooks' note: Toasts may be made one day ahead and kept in an airtight container at room temperature.