Preheat an oven to 180ºC
Grease the square tin and line with parchment paper
Fit the K beater to the machine
Add Ingredients 1 (butter, sugar) into the Mixer bowl
Attach the Mixer bowl to the machine and fit the splash guard
Mix on speed Max for about 2 minutes until light and fluffy
Add Ingredients 2 (eggs, vanilla) to the Mixer bowl
Mix on speed Max for about 2 minutes until incorporated
Add Ingredients 3 (baking powder, flour, milk) into the Mixer bowl
Mix on speed Max for about 1 minute until combined
Pour the batter into the square tin
Bake at 180ºC for 25 minutes until golden
Remove from the oven and let cool
Add the first two items of Ingredients 4 (icing sugar, water) into the large bowl
Manually mix to form a thick icing
Pour onto the cake and spread until covered
Sprinkle the last item of Ingredients 4 (sprinkles) over the top of the cake
Leave until the icing is set
Cut into squares