For the blackberry tiramisu, first mix the egg yolks with the powdered sugar until fluffy. Add the mascarpone and blackberry puree and mix again briefly.
Layer half of the sponge cake in a baking dish and spread half of the blackberry cream on top. Layer the second half of the biscuits on top and spread with the rest of the blackberry cream.
Chill for a few hours. Garnish with fresh blackberries before serving. Makes 6-8 pieces.