Whisk egg yolks, wine, sugar, and lemon juice in a bowl for one minute.
Place bowl over simmering water and whisk for 8 minutes until fluffy.
Chill the sauce over ice while whisking, then refrigerate overnight.
Mix egg yolks and sugar on high speed for four minutes until pale.
Add flour, baking powder, and salt and mix on low for two minutes.
Mix in butter for one minute, then chill the dough on a tray for 35 minutes.
Preheat oven to 160°C.
Roll dough to 3mm thickness between paper and freeze for 15 minutes.
Cut dough into four 5cm x 15cm rectangles and bake for six minutes.
Trim shortbread edges immediately and set aside to cool.
Macerate plums, sugar, liqueur, and lemon juice for one hour.
Boil half the plums in the liquid, then add raw quartered plums and cool.
Assemble by placing three plums on a shortbread biscuit.
Top with sabayon, dust with icing sugar, and caramelise with a blow torch.