Spread the raspberry jam evenly over the sponge or Savoiardi biscuits.
Whisk the eggs with the sugar and vanilla essence. Heat the milk to the ‘shivery’ stage and add it to the egg whisking all the time. Put into a heavy saucepan and stir over a gentle heat until the custard coats the back of the wooden spoon lightly. Don’t let it boil or it will curdle.
Cut the sponge into ¾ inch slices and use these to line the bottom of a 3 pint (1.7litre) glass bowl, sprinkling generously with sherry as you go along. Pourin some homemade egg custard and then add another layer of sponge. Sprinkle with the remainder of the sherry. Spread the rest of the custard over the top. Cover and leave for 5 or 6 hours, or overnight, to mature.
Before serving, spread the whipped cream over the top and decorate the trifle. Berries of course fresh raspberries, strawberries or blueberries are the best.