Heat the oven to 180°C. Grease the cake pan. Attach the baking paper to the bottom for better manipulation later.
We will need 3 cake layers. Start by mixing ingredients for the first cake layer. Whisk together 3 eggs, 90 g white crystal sugar, and 90 g cake flour. Bake for 10 minutes.
Repeat the process one more time with another cake layer.
Now for the third cake layer. This layer will be thicker so you will mix 5 eggs, 150 g white crystal sugar, and 150 g cake flour. Bake for 14 minutes.
Once the cake layers are cool, take the thickest one and cut it into smaller pieces by knife. Put the pieces into a bowl and add rum and fruit syrup. Mash the wet cake layer in your hands until it's very soggy.
Now the next step is optional - you need this wet cake mixture to be pink/red enough. You can use more red fruit syrup, add red food coloring, or boil the frozen forest fruit. Then you can use the red water from the boiled fruit to color your cake. It's up to you.
Now you have 2 perfect cake layers and one wet red cake mash. Put one of the clean layers into the cake pan, and spread a thin layer of extra jam on top. Continue by adding wet red cake mash. Smoothen the cake with a rubber spatula. Put another cake layer on top.
Now you should have a solid-looking cake. Now the fun part - you have to weigh the cake down by putting something heavy on top. I usually use a big pot with a little bit of water in it, that perfectly sits on the cake. Now put the cake into the fridge for 30-40 minutes.
Now let's make the glaze. Pour the icing sugar into the bowl. Whisk the icing sugar by using an egg whisker, and slowly pour the boiling water into the bowl. The consistency should be thick as the American pancake batter. If it's too runny - use more sugar. If it's too thick - add more boiling water. Use a few drops of red food coloring or the red water from the forest fruit. You want to reach the perfect pastel pink color.
Put the cake into the fridge overnight. After this time it should get really moist, juicy and the taste of rum will hit you in the morning.
Cut the cake into the shape of a heart by using boiling water and a knife. Put the knife into the tall glass with boiling water so the glaze won't crack while cutting the cake.