I made a simple vanilla cake and ensured that I have 8 cups of batter. I divide batter evenly between three bowls and color 2 of them in pink.  I use the same food color for each (Wilton gel color in pink).  I color one dark pink and one light pink.  The third bowl I keep as is.

For between the layers and to pipe the tulips, I prepared buttercream (about 250g of butter with 500g powdered sugar and some vanilla extract).

My baking pans are each 35 cm long and 25 cm wide.  I cut out circles with a diameter of 10 cm. 

My recipe for american buttercream can be found here: http://www.keyk.de/en/blog/baking-recipes-and-ideas/classic-american-buttercream-recipe