This is a British version of the classic Italian dessert of eggs, sugar, and wine beaten to a frothy mousse; I've used perry here instead of Marsala. In posh restaurants zabaglione was traditionally made in front of you at the table. If you have a portable gas burner and a nice copper bowl and want to show off to your dinner guests, you could try it at home – but not if I'll be held responsible.
For the zabaglione
4 medium egg yolks
5tbsp caster sugar
A third of a vanilla pod, split and the seeds scraped out
To make the zabaglione, put the egg yolks, sugar and vanilla seeds in a round-bottomed steel or Pyrex bowl (not aluminium or it may go a nice grey colour). Beat well with a whisk for 2-3 minutes then mix in the Marsala.
Hold the bowl with a cloth and f rest it over a pan containing 3-4cm of simmering water. Whisk continuously for a few minutes (use an electric whisk if you prefer) until the mixture is thick and frothy.
To serve, put the blueberries in bowls or plates and pour over the warm zabaglione.