To make the frosting – whip together room temperature butter, vanilla extract and cream cheese using a hand mixer until thoroughly combined and smooth. Add the icing sugar in thirds, mixing well between each addition to ensure it gets thoroughly mixed in.
Cover and set aside in the fridge while you make the cake
Beat room temperature butter with the caster sugar in a stand mixer using the paddle attachment until light and fluffy and pale
Add one egg at a time and continue to mix. It is normal for the mixture to look split at this stage
Add the vanilla extract and the butter milk and mix
Add the sifted flour and baking powder in thirds, mixing well between each addition
Once the batter has come together, add to a well greased and lined baking tray and even out with a pallet knife
Bake at 180℃ for 30 minutes (see note) until a skewer comes out clean and the cake is golden
Let cool completely before spreading the frosting over the top
Add 2 tablespoons of sprinkles before cutting and serving
Notes
Note - if you use a larger baking tray the cooking time will be less. I recommend checking your cake after 20 minutes to see if it is close to being ready using a skewer. If it comes out clean, it is ready.