Mix the 4 egg yolks with 2.1 oz of sugar.
Whip the 4 whites into peaks with 21 oz of sugar.
Soften the gelatine in cold water.
Whip the cream.
Combine the whipped cream with egg yolks.
Melt the gelatine in the coffee and add to the mixture.
Add the whipped whites by stirring from the bottom up.
Pour the mixture into a rectangular plumcake mould.
Cover it with the slice of sponge cake and soak it with the sweetened coffee.
Place in the freezer for 6 hours.