Step 1Remove skin of pummelos and cut into thin strips. You want just surface of rind, not white pith. Blanch approximately 1/4 cup of rind strips in simmering water 3 minutes.
Step 2Clean pith from pummelo segments, then remove membranes. Arrange segments around edges of 6 dessert plates. Place blueberries, raspberries and strawberries in center of each plate.
Step 3Mix together egg yolks, 3 tablespoons sugar and 1 cup champagne. Whisk mixture together in top of double boiler set over, but not touching, simmering water until consistency thickens and ribbons form, about 6 minutes. Add blanched zest, optional, to sabayon and spoon evenly over fruit. Dust with powdered sugar and serve.