1 package vanillasugar
1 package baking powder
200g white chocolate couverture (minimun)
~200g jam (I chose strawberry, cherry and quince)
food coloring (red, yellow, green, blue)
1. Make a dough of the butter, sugar, vanilla suger, eggs, flour, baking powder and milk. All together it should be about 1kg of dough. When it's ready, divide it into 7 even pieces. If you don't have that many bowls, you can as well take 100-150g for each layer, one after another.
2. Grease your baking form. Then it's time for the first layer of color! Mix red into your first 100-150g of dough, the more food coloring you use, the more intense the color should get. Spread it evenly inside the baking form and let it back for about 10 minutes with 150°C.
3. During that time, you can already prepare the second layer, using another 100-150g of dough and mixing it with red and yellow food coloring to make orange.
4. When the first layer is done baking, put it out, let it cool down a bit and put a thin layer of jam on it. Grease the baking form again and put the second layer in it, and let it bake again for about 10 minutes.
5. Now you can prepare the third layer using only yellow food coloring. When the second one is out of the oven, let it cool down, put it onto the first, and add another layer of jam. Grease the baking form again, put the third layer in it and let it bake again for 10 minutes.
6. Prepare the fourth layer with green food coloring. Let the third layer cool down, put it onto the other two, and add, once again, another layer of jam. Bake the fourth layer and prepare the fifth with blue food coloring.
7. When the fourth is done, let it cool down again, put it onto the other three and add another layer of jam! Bake the fifth layer and prepare the sixth. You can either make a darker blue, or, if you don't have enough dough left, make the violet one with red and blue.
8. Put the fifth layer out of the oven, let it cool down, put it onto the others and add another layer of jam. Put the sixth one in the oven and, if you have dough left, prepare the seventh and last layer with violet.
9. Proceed with the same steps like with the other layers, and bake the last one, then add it as well, but on the last layer should be no jam on top!
10. When all is cooled down, you should prepare the couverture. Let it melt in a waterbath, then let it cool down a little bit, but not let it get hard again. Then spread it evenly on top of the cake, and onto the side as well. Make sure to put decorations on it before it dries! It can be a bit messy, so you really should try to let the molten couverture cool down a bit.
As for the jam, you can use different ones, or only one, depending on how "fruity" you want to have the cake. In this case I used strawberry jam for the first two layers, the the quince one for two layers, and the cherry one for the too last, to match the colors a little bit.
The food coloring shouldn't be tasted, so don't use too much of it! But I found out that especially red needs more of it than the others, while blue is the strongest coloring. The un-colored dough already has a somewhat yellowish color, so you should put that into account when you color your layers. You can also put them in different orders, or make other colors, however you want!
Another possibility is to color all 6-7 layers, then put it into the baking form all together, next to each other or on top of each other. This should get a somewhat of a marbled cake.