Put the flour, sugar, baking powder, salt and butter in a freestanding mixer with a paddle attachment, or use a handheld whisk. Beat on a slow speed until you have a sandy consistency
Gradually pour in half of the milk, and beat until the milk is just incorporated
Whisk the egg, vanilla extract and remaining milk together in a separate bowl. Then pour the liquid into the flour mixture and beat until just incorporated. Scrape down the sides, and beat for a few more minutes. It’s important not to over-mix the batter
Spoon the mixture into the paper cases until two-thirds full, and bake in the preheated oven for 20-25 minutes, or until light golden and the sponge springs back when pressed. A toothpick inserted into the centre should come out clean
Cool on a wire rack, and ice with frosting and sprinkles once cool
For the frosting, beat the icing sugar and butter together with a handheld whisk or free standing mixer with paddle attachment, until the mixture comes together
Turn the mixer down to a slow speed. Combine the milk and vanilla extract, and add to the mixture a few tablespoons at a time
Once incorporated, turn the mixer speed up and beat for about 5 minutes, or until the frosting is light and fluffy. Then use food colourings to create whatever shade you like!