Vibrant Rainbow Birthday Layer Cake

1. Cream together butter, sugar, and vanilla sugar

2. Add eggs one at a time, mixing well after each addition

3. In a separate bowl, whisk together flour, baking powder, salt, and lemon zest

4. Add the dry ingredients and milk to the batter alternately, mixing until smooth

5. Divide the batter evenly among 6 bowls

6. Add a few drops of food coloring to each bowl: use red, yellow, green, and blue; for orange, mix 1 drop red and 3-4 drops yellow; for purple, mix 1 drop blue and 3-4 drops red

7. Grease a 20 cm springform pan and preheat the oven to 180°C (160°C convection)

8. Pour one colored batter into the pan and smooth the top

9. Bake for 15 to 20 minutes

10. Let the cake cool in the pan, then remove and let cool completely

11. Repeat with the remaining batters, greasing the pan before each layer

12. Beat cream cheese, soft butter, and powdered sugar until smooth

13. Place one cooled cake layer on a serving plate and spread a layer of filling over it

14. Add the next layer and repeat until all layers are stacked

15. Frost the top and sides of the cake with the remaining filling

16. Decorate with colorful sprinkles

Tips

1. To help the thin cake layers release easily, line the bottom of the springform pan with a round piece of parchment paper for each layer