Method:
1 Preheat oven to 220°C. Line a baking tray with baking paper.
2 Cut the pastry sheet into four squares. Score a border 1.5cm wide around the edge of each square. Transfer to the prepared tray.
3 Process egg, butter and nuts to create a paste. Spread over each pastry within the border.
4 Arrange the grapes on top of nut paste and sprinkle with sugar. Bake in the oven for 5-6 minutes or until golden.
5 Whisk egg yolks, wine and extra sugar in a bowl placed over a saucepan of simmering water and whisk continuously for 5-6 minutes or until mixture has doubled in volume.
6 Place tart on a plate, top with sabayon. Serve