Preheat your oven to 175°C / 350°F. Line two 8-inch cake tins with baking paper and set aside.
Add the flour, corn starch, baking powder and salt to a medium sized mixing bowl and mix using a whisk. Set aside.
Add the sprinkles to a small bowl along with 2 tbsp of the dry ingredients and use a spoon to mix together. This will help prevent the sprinkles from bleeding color and also from sinking to the bottom. Set aside.
To a separate large mixing bowl add the softened butter and sugar. Use a hand meld electric mixer to cream together for about 3minutes.
Scrape down the bowl using a spatula and then add the eggs one at a time, mixing each time until well combined. Then add the vanilla extract and mix.
Add half the dry ingredients and half the milk and mix on low speed. Add the remaining ingredients and repeat.
Add the sprinkles and fold through.
Split the batter between two 8-inch cake tins that have been lined with baking paper. Bake for 30 minutes. Allow to cool for 5 minutes and then take out of the cake tin to allow to cool completely to room temperature.