Heat the oven to 175 °C. Melt the butter and chocolate. Whisk the eggs and sugar lightly. Add the butter and chocolate mix to the eggs. Combine the flour, baking powder and salt and fold into the batter. Divide the batter into two baking tins lined with SAGA Baking Paper, and bake for about 20 minutes or until the batter is firm around the edges, but is still a little soft in the middle. Let the bases cool fully.
Next, prepare the filling. Soak the gelatine sheets in cold water. Remove the flesh from the mangoes and cut it up into a bowl. Add the sugar and blend to a smooth mixture. Drain the excess liquid from the crushed pineapple.
Whisk the mascarpone and whipping cream to a soft foam. Mix in the mango. Heat the mango-passionfruit juice and dissolve the soft gelatine sheets in it. Pour the gelatine mix into the mango foam while mixing continuously. Fold in the drained pineapple.
Place the first base on a serving dish. Line the ring of a springform cake tin with baking paper, and place the ring over the base. Pour half of the filling onto the base. Lift the second base carefully on top, and then pour on the rest of the filling. Let it set in the refrigerator until the next day.
For the icing, whisk the cream, mascarpone, icing sugar and food colouring. Ice the cake. Mix the cocoa powder into a little hot water and splash this "cocoa paint" on the cake with a brush.
Make the bird's nest decoration by lining a small bowl with baking paper. Chop the pretzel sticks into pieces a few centimetres long. Melt the chocolate and pour on the pretzel sticks. Lift the pretzel sticks into the bowl in small batches to make a bird's nest. Let it set in the refrigerator for about 15 minutes. Lift the nest onto the ready cake and finish with the Easter eggs.