Let the cake cool down well, and do the cream. Whites need to beat white with a mixer or blender. Continuing to beat, add sugar, followed by corn starch. If you will take potato starch, then take exactly half of it. Thanks to the starch, the juice from the berries will not spread. We spread the protein mass in a bowl, add the berries carefully to it and distribute them by weight with a spatula. The cake has cooled down, put the protein mass with berries in it and put it in the preheated oven to t-180 C for another 15 minutes. The cream should set. The pie is ready.