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Line the base of a 900 g/2 lb loaf tin (pan) with
greaseproof (waxed) paper. Line the base and sides
with some of the sponge fingers.
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Sprinkle the gelatin over the water in a small bowl and leave to
soften for 5 minutes. Stand the bowl in a pan of
hot water and stir until the gelatin has dissolved
completely (or heat briefly in the microwave).
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Blend
the sugar with the custard powder, a little of the
milk and the egg yolks in a saucepan. Blend in all
but 15 ml/1 tbsp of the remaining milk and
half the cream.
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Break up the chocolate and add to
the pan. Bring to the boil and cook for 2 minutes,
stirring, until the chocolate has melted and the
mixture has thickened. Stir in the dissolved gelatin. Leave until cool and beginning to set.
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Pour half the mixture into the lined tin. Cover with
a layer of the remaining sponge fingers. Add the
remaining chocolate mixture, then a layer of sponge.
Chill overnight.
-
Turn out on to a serving plate and
remove the paper. Melt the Mars Bar in a saucepan
with the reserved 15 ml/1 tbsp milk. stirring
all the time. Spoon over the sponge fingers.
-
Whisk
the egg whites until stiff, then the remaining cream
until peaking. Fold the egg whites into the cream.
-
Spread all over the cake and decorate with a few
chopped walnuts. Chill again before serving.