Take mascarpone cream cheese in a bowl and whisk it till smooth. Add coffee decoction, 2 tbsps melted chocolate and whisk together. Add the melted gelatin and mix. Fold in whipped cream and keep the bowl in a refrigerator to set.
Boil sufficient water in a deep non-stick pan, place a fitting bowl on it. Put egg yolks in the bowl, add the sugar and whisk for 3-4 minutes or till the sugar melts and the mixture becomes light.
Halve the chocolate sponge horizontally. Cut 4 pieces with a rectangular cutter mould. Keep the pieces at the base of 4 rectangular moulds. Arrange most of the strawberry pieces over the cake and chill for a while.
Cool the egg yolk mixture slightly and fold into the mascarpone cream mixture and chill again. Pour this mixture over the cake pieces and keep them in the refrigerator to set. When completely set unmould them onto a serving plate.
Drizzle the remaining melted chocolate over them and sprinkle cocoa powder through a small sieve.
Decorate with the remaining strawberry slices and serve immediately.