Preheat the oven at 190 Celsius degrees.
Mix butter and sugar with a stand mixer until creamy consistency. Add slowly melted chocolate and keep mixing until well incorporated. Take cocoa powder and stir it into flour, stir well to break all cocoa powder lumps. Now start adding flour mixture and sparkling water while constantly mixing, add a bit of both of them at the time (if you use a hand mixer then simply add one after another while constantly mixing). Set aside.
Mix aquafaba with 1.5 tbsp. of sugar into a fluffy foam. Now add this foam into a previous cake batter mixture by using a spatula, it should be incorporated well into the batter.
Pour cake batter into a cake mold covered with baking paper and bake it at 190 degrees Celsius for 25-30 min. Let it cool down completely then cut it in half with a sharp knife.
Warm up marmalade until boiling point, remove from heat and stir a bit. Fill the bottom part of the cake with half amount of marmalade, then place the second half on top of it. Fill the surface and sides of the cake with the rest of marmalade. Set aside.
Melt together ingredients for chocolate ganache while constantly stirring. Cover the whole cake with prepared warm ganache and set it into the refrigerator. Serve cold with a bit of vegan whipped cream.