Slice the cake. With a small glass, cut out rounds in the cake and sprinkle each round with a teaspoon of sherry. Make sure that you have twice as many cake rounds as glasses. Prepare the custard. Stir in half of the fruit. Leave to cool. Place a slice of cake in each glass. Cover with a spoonful of cream-fruit mixture and top with a second slice of cake. Cover with another spoonful of cream-fruit mixture. Seal all glasses with plastic wrap and place them in the refrigerator for at least 2 hours to set. In the food processor, purée the other half of the fruit with the sugar and strain. Collect the coulis (sauce) in a bowl and pour it into a decanter. Before serving add a dash of coulis to each trifle, covering the top of each glass with an even layer.