1 The day ahead of serving, split each cake in half; brush the cut edges with syrup. Lightly crush half the raspberries. Put the base of each cake on a cake board, then spread each with a layer of raspberry coulis. Scatter over the crushed raspberries followed by a thin layer of Creme patisserie (about one-third of the total amount). Cover with the other halves of the cakes, then chill.
2 Select about 6-8 long strands of redcurrant. Lightly beat the egg white and put the sugar in a shallow bowl. Brush redcurrants lightly with egg white, then coat lightly with sugar and arrange over a flat tray lined with baking paper. Leave overnight to dry out.
3 Spread Creme patisserie thinly over the tops and sides of the cakes. Measure the depth and circumference of the small cake, then roll one-third of the modelling paste into a sausage. Put this shape between two large sheets of baking parchment, then roll to the circumference of the cake and about 3-4cm more than the depth. If the paste splits, put it in the food processor with 1 tbsp oil and whizz it up, then re-knead and it should come back again to a smooth paste. Once rolled sufficiently, flip the whole lot over and peel away the uppermost sheet of paper. Trim the base of the paste in a straight line, leaving the top wavy. Carefully wrap the modelling paste round the cake with the straight edge to the base, pressing in the sides, then peel off the parchment. Repeat with remainder of paste for the larger cake.
4 Cut the dowels into equal lengths, about 2 cm more than the depth of the larger cake, then insert 4 into the centre of the cake in a square formation, just smaller than the size of the smaller cake, then put two in the middle. On the day, place the smaller cake on top of the larger one, then fill around the edge of the large cake and the top of the small cake with the berries, finishing with the frosted redcurrants. Dust with icing sugar.