Start with the chocolate shortcrust pastry. Cut the butter into small cubes. Put flours, cocoa, icing sugar, salt and butter cubes in a blender. Blend it together quickly, add the egg and mix to a firm dough.
Roll the dough between two pieces of wax paper and let it rest in the refrigerator for minimum 1 hour. Line a spring-form pan (20 cm in diameter) with dough, and set the bottom in the fridge.
Crumble excess dough with your fingers. Distribute the crumble on a baking sheet lined with baking paper and bake at 175°C (350 F) for about 10 minutes until it is slightly golden. Let it cool completely.
Continue with the rhubarb frangipane. Cut the rhubarb into small pieces and spread them on the chocolate shortcut pastry.
Mix almond flour, sugar, butter, eggs and Amaretto in a bowl and whip it light and fluffy. Pour the frangipane batter on top of rhubarb, and smooth the surface with a spoon.
Bake the pie for about 25 minutes at 175°C (350 F) until it´s nice and golden. Let it cool completely.
Move on with rhubarb mousse. Peel and divide rhubarb into small pieces. Cook the rhubarb with sugar. Strain through a sieve.
Put the gelatin leaves in cold water for a few minutes. Melt them in the hot rhubarb liquid. Let cool.
Whip the double cream, and add it to the rhubarb liquid. Pour the mousse in a spring-form pan (16 cm in diameter) covered with plastic film. Put it in the freezer for minimum 2 hours or overnight.
Place the frozen rhubarb mousse on top of the pie and let it thaw in the refrigerator for minimum 2 hours.
Spread a little crumble and green leafs in the edge of the pie and top it with fresh berries.