In a large bowl, combine together flour, cocoa powder, sugar, baking powder, salt and baking soda. In a separate small bowl, mix curd or buttermilk, oil, food color of your choice, vinegar, vanilla extract and apple sauce.

Stir the wet ingredients into the dry ingredients bowl until just mixed. I added another teaspoon of curd to adjust the consistency. Pour the batter into prepared pan. Bake for 20-25 minutes or till the tooth pick inserted near the centre comes out clean. Cool the cake completely in the pan. Repeat for remaining 6 layers in colors of rainbow.

Prepare ½ kg ganache. Place the violet layer at the bottom, soak in sugar syrup and spread ganache. Repeat. After stacking 3 layers, insert 3-4 straws, or wooden dowels inside the layers to support the other 4 layers. Once all the 7 layers are stacked, insert another set of straws to further stabilize the cake. When making tall or tiered cakes, straws or dowels are must. Crumb coat with whipped cream. For fresh flowers, thoroughly clean and dry them. Stick the bunch together using an elastic band. Now place them on a small portion of butter paper cut in the size of flowers so that it's not visible. If you are planning to insert the stem inside the cake, it is best to insert using straws or cling wrap them. Use the remaining ganache to drip on top. Or Assemble and decorate as per your choice.