Delightfully modern this impressive cake is perfect for the summer months.
For the cake, preheat oven to 180°C. Grease 2 x 6inch spring form pans and 2 x 8 inch spring form pans and line the base and sides with baking paper. Beat butter, zest and sugar until light and fluffy in an electric mixer. Add the eggs 1 at a time mixing well after each one is added. Sift the flours together. Stir in sifted flours, add milk and sour cream, mix well. Pour half of the batter between 1 of the 6 inch and 1 of the 8 inch pans. Then add about ¼ teaspoon of the lemon yellow colour to the remaining half, mix well and divide between the remaining 2 pans. Bake for about 30 mins, because you have 2 different sizes of pans in the oven you will need to keep an eye on the smaller pans. The cakes are ready when a skewer inserted into the middle comes out cleanly. Repeat the whole process for the remaining 4 cakes. Once the batter is made add about a teaspoon of the yellow colour, mix well and pour half of the batter between 1 of the 6 inch and 1 of the 8 inch pans. Add another ½ teaspoon of the yellow to the remaining half (you may need to add more colour to ensure these last 2 cakes are the deepest yellow of them all), mix well and divide between the remaining 2 pans.
For the buttercream, whisk the egg whites and sugar over a pan of simmering water until the mixture reaches 115°C. Pour the mix into an electric mixer with a whisk attachment.
Whisk until glossy and peaks are very firm. Add the icing sugar and mix on low until incorporated then on high until mixed well. Add the butter, shortening and vanilla until mixed in well.
Assembly, when cakes are cool, level the tops of all of the cakes. Place the darkest yellow cake onto a 8inch round cake board, spread with buttercream, grate some lemon zest over and add the next lightest yellow cake. Repeat until all 4 8 inch cakes are stacked. Do the same with the 6 inch cakes.
Cover the tops and the top third of the sides of each cake with the white butter cream. Then add a few drops of yellow colour to the remaining mix. Spread this colour around the middle third of each cake. Then add a few more drops of yellow colour to the last of the buttercream and spread around the bottom third of each cake. Roughly smooth the sides and refrigerate for a few minutes to allow the buttercream to set a little. Take the cakes out of the fridge and smooth the tops and sides (it is ok if some of your cake shows through the icing, this is pretty trendy right now!)
Inset 3 or 4 straws into the 8 inch cake around the centre of the cake and cut the tops off about 1 mm above the level of the top of the cake. Place the 6 inch cake on top of the 8 inch cake. Decorate with fondant flowers (or any decoration you like).
This recipe has not been edited or tested by the Bake Off Food Department.