Preheat oven to 350F(180oC). Grease and line 2x 6-inch cake tins.
On your KitchenAid Mini Stand Mixer gently mix together the flour ,both sugars, baking powder, baking soda and salt.
In a large microwave-safe bowl, melt the butter in the microwave.
In a separate jug, whisk the egg, buttermilk, and vanilla extract until combined.
Turn on your KitchenAid Mini Stand Mixer and pour in your wet ingredients and melted butter. Mix just until the batter comes together. The batter will be thick. Once baked, cool on a rack.
Lastly, stir in the sprinkles but do not over mix because the sprinkles will bleed their color.
Pour batter into prepared cake pan. Bake for 35-40 minute or until a toothpick inserted in the center comes out clean. Allow to cool.
Using a whisk attachment beat softened butter on medium speed with an electric or stand mixer. Beat for 3 minutes until smooth and creamy. Add sifted powdered sugar one spoonful at a time until all the sugar has been incorporated.
Now add in your food coloring (if desired) and milk. Increase to high speed and beat for 3 minutes until your frosting is light and fluffy.
Level your cakes by carving off any bumps on the top of your cake. This will make it nice and even.
Using a palette knife, spread some frosting on one side of cake to create the filling. Lay the other cake on top and spread more frosting on top. With your palette knife, run it around the filling coming out the sides of the cake to create a smear of frosting to give it a rustic look. This is a "naked" cake so you don’t need to decorate it all over.
Decorate with some more sprinkles around the top of the cake.
Enjoy straight away or store at room temperature for up to 4 days.