Preheat the oven to 350 F. Grease and line 12 and then 4 (16) cupcake tins with liners. Set aside.
In a stand mixer bowl with a whisk attachment, beat the softened butter and oil together until completely combined together with no lumps. The butter has to be soft, if it’s too cold there will be lumps. Add the sugar to the oil and butter and beat on high until light and fluffy. Add the eggs in one at a time, once all eggs are incorporated add vanilla extract. Beat the mixture for about 2 minutes to incorporate as many air bubbles as possible.
In a medium bowl whisk together the cake flour, salt, and baking powder, pour into stand mixer bowl along with the other ingredients, mix slightly while flour pieces are still visible. In a small bowl, mix together milk and mayo. Pour mayo/milk mixture in with the other ingredients. Mix until all ingredients are just combined. Fold in the sprinkles until they’re well distributed.
Use a 1/4 cup measuring cup to distribute the batter evenly into the prepared cupcake liners and bake for 20-27 minutes or until the cupcakes are barely light golden and spring back when pressed. Transfer to a cooling rack immediately. Let the cupcakes cool before frosting with your favorite frosting!