Defrost puff pastry slices at room temperature for about 20 minutes. Lightly whisk the egg white with a fork. Halve slices and brush with egg white. Fold the corners into the middle and press down firmly. Line the middle of the puff pastry slices with baking paper and spread the dried peas on top.
Place 6 cakes on a baking tray lined with baking paper and bake in a preheated oven (electric range: 225°C/ gas: level 4) for 12-15 minutes. Let the cakes cool down on a grid. Remove baking paper and peas from the cake. Bake the remaining cakes in the same way. In the meantime, drain the cherries on a sieve, collect the juice and measure 1/4 litre. Stir 3 tablespoons of cherry juice, 1 packet of sauce powder and 20 g sugar until smooth. Bring the remaining juice to the boil, stir in the sauce powder, bring to the boil again, add the cherries and stir in. Fill 1 tablespoon of stewed cherries into the middle of each cake. Mix 3 tablespoons of milk, remaining sugar and remaining sauce powder. Bring the remaining milk to the boil, stir in the sauce powder and bring to the boil again while stirring.
Bring the remaining juice to the boil, stir in the sauce powder, bring to the boil again, add the cherries and stir in. Fill 1 tablespoon of stewed cherries into the middle of each cake. Mix 3 tablespoons of milk, remaining sugar and remaining sauce powder. Bring the remaining milk to the boil, stir in the sauce powder and bring to the boil again while stirring. Let cool and stir in mascarpone. Also fill the cakes by the spoonful and dust with icing sugar. Serve decorated with lemon balm as desired