These are both pretty and colourful! And they taste really good too. You can make them in a proper sized cake pan, or cupcakes.
You can make buttermilk at home. Take 1 cup room temperature milk and add 1 tablespoon vinegar or lemon juice. Let this stand for 5-10 minutes and then use accordingly.
Preheat oven to 170C.
Line your cupcake pans with cupcake liners and set aside.
Sift together flour, salt and baking powder. Set aside.
Cream butter and sugar until light and fluffy. Scrape sides of bowl every few minutes using the whisk attachment or a rubber spatula. This is crucial. Otherwise you're going to be left with chunks of butter in your finished batter. So make sure you cream it well and don't rush! :)
Add eggs one at a time. Making sure each egg is perfectly incorporated before you add another. If you skip too quickly past this stage, you will have a cake that smells of eggs because the bits of egg that aren't fully beaten in will bake separately in the cake and it will be like having scrambled eggs cooking in your cake, eww! So incorporate the eggs whenever you reach this stage for any cake recipe!! Remember to scrape down the sides of the bowl after every few eggs. Add vanilla.
Add flour and buttermilk in three alternative pours, starting and ending with flour. Mix on slow speed and scrape the bowl during the process. I know, it's a pain in the butt. It's worth it. At this stage do NOT over mix, just combine until the batter is incorporated. Over mixing can ruin your cake.
Once everything is well incorporated, use a plastic spatula to fold the batter a few more times to make perfectly sure you've got everything will mix.
Divide the batter between as many bowls as you have colours. Add a few drops of colour to each bowl and mix. Remember, the color your batter looks will be the same colour your cake will be.
Now fill your cupcakes, dropping in a spoonful of each colour one on top of the other until the cups are two-thirds full. Bake in preheated oven for 15-18 minutes or until a toothpick comes out clean when stuck into a cupcake.
Turn the cupcakes over on a rack and let them cool to room temperature before frosting them, or you can leave them plain. You can add colors to your frosting and make it a rainbow frosting as well. :)