The best thing about birthdays is cake!
My girlfriend Fi & I used this recipe from whisk kid for a joint birthday surprise ...
2 sticks (226 g) butter, room temp
2 1/3 cups(426 g) sugar
5 egg whites, room temp
2 teaspoons vanilla
3 cups(426 g) flour
4 tsp baking powder
½ tsp salt
1 1/2 c (355 ml) milk, warmed for 30 sec in microwave
Red, blue and yellow gel food colouring (mix together to make purple, green & orange) - liquid will not be vibrant enough
Preheat the oven to 180C . Oil and line how ever many 9 inch cake pans you have (we re-used two). Sift together the flour, baking powder and salt . Set aside . Cream the sugar and butter, then slowly add the egg whites . Add the vanilla and mix until fully incorporated . Then, alternating between wet and dry, add the milk and flour mixture in two parts . Divide the batter amongst 6 bowls - about 1 cup each . Whisk a fair amount of the appropriate food color into each bowl . Keep in mind that the color of the unbaked batter will be the color of the baked batter. Pour into the pans and bake for 15 minutes each . When you remove them from the oven, let them rest on the cooling rack, in the pan, for ten minutes . Then flip, cover, and stash them in the fridge to cool quickly .
Assembling the cake is a little tricky as the layers are quite thin . Make sure you have plenty of icing to go in between the layers and over the whole cake a few times so that it is prefectly white with no coloured crumb clues! Any icing would work - we used a buttercream icing for the layers and a royal icing for the outside.
The looks on their faces say it all!
>>> I have also read about people using cheap packet cake mixes and adding the gel colour. Check out this 30-layer masterpiece!