Preheat oven 325 degrees F.
Combine all ingredients for the crust. Butter eight 3 inch tartlet moulds that are about 1 inch deep. Press the crust firmly into each mould so that the crust comes right up to the edge. Place on a cookie sheet and bake for 10 to 13 minutes or until golden and crisp. Tarts will puff up when ready. Remove from oven and poke gently with a fork to deflate. Cool slightly for about 10 minutes. Remove shells from moulds. Prepare sabayon.
Combine ingredients for sabayon in either a large stainless steel bowl or the top of a double boiler. Place over gently simmering water. Whisk vigorously for about 7 to 9 minutes or until sabayon becomes thick and ribbon like.
To assemble the tarts, pour a little melted chocolate in the bottom of each tart shell. Let cool slightly. Divide the sabayon equally among tarts and top with sections of fresh grapefruit.