In a bowl cream together butter, sugar and cream cheese until light and fluffy. Add the eggs and vanilla until creamy. In another bowl, combine all the dry ingredients and mix with a fork or whisk to break up any lumps.
Add the dry ingredients slowly (about ½ cup at a time) into the wet ingredients and stir until thoroughly incorporated before adding more. Continue until all ingredients are mixed.
Using a spatula or a knife, spread the batter on a 9 x 13” baking sheet lined with parchment paper. Place in a preheated oven at 350 degrees F for 20 minutes, or until a toothpick comes out clean in the center.
Place on a cooling rack and allow to completely come to room temperature. To make the frosting, cream the butter and cream cheese with the vanilla until light and fluffy. Add in the powdered sugar and mix until frosting is smooth and without lumps.
Once bars are completely cooled off, spread the frosting over the top in an even layer and add desired sprinkles.