Preheat the oven to 190°C/Fan 170°C/Gas 5). Separate the eggs. In a bowl, beat the egg yolks and 60g of the sugar with 10 tablespoons of water and the orange zest using an electric whisk until thick and foamy. Whisk the egg whites with the salt until stiff, trickling in the remaining sugar as you go. Gently fold the whisked egg whites into the yolk and sugar mixture. In another bowl, combine the almonds, cornflour, and baking powder and sift this over the egg mixture. Fold in briefly using a balloon whisk.
Grease just the bases of two springform tins (diameter 20cm/8in) with butter and dust with cornflour. Divide the cake mix equally between the tins, smooth the surface, and bake in the centre of the oven for 18–22 minutes, until the cakes have risen and are golden brown in colour. When an inserted wooden skewer comes out clean, they are ready. Release the cakes from the tins and leave to cool completely on a wire rack.
To make the filling, stir together all the ingredients except the berries. Place one of the cakes on a cake platter. Spread two-thirds of the cream over this base. Cover with berries, then put the second cake on top and spread over the remaining cream.
Decorate the cake, as desired, with berries and blackberry flowers. Chill in the fridge for 30–60 minutes before serving.