Make the buttercream: in a small bowl, use a hand mixer to beat the butter with the salt and vanilla until light and fluffy, at least 3 minutes. Add the powdered sugar and beat to combine. Add 1 TB of the milk and if it doesn’t smooth out, add another TB. Set the buttercream in an airtight container until cake is ready to be assembled.

Preheat oven to 325 and butter and flour an 8×8″ square pan.

In a bowl, beat the butter, oil, salt and vanilla with the sugar until very light and fluffy, 3-5 minutes.

Add the egg whites one by one, allowing the first to fully incorporate before the second. Beat until very fluffy.

Add the cake flour, baking soda and powder and buttermilk all at once and beat to combine.

Fold in the sprinkles and chocolate chips, if using.

Pour into cake pan and bake for 30-35 minutes, until a cake tester comes out clean from the center.

When the cake is completely cool, use a ring to punch out four circles (this is easier to do if the cake has been frozen for a bit). You now have four tiny cake layers. Level them with a cake leveler or knife so they are the same height.