Be sure to use mini chocolate chips in the cake batter. They will disperse and suspend best; larger chocolate chips will sink to the bottom of the pan.
Fine grain caster sugar is recommended for the boiled frosting as it dissolves easily. You can usually find this in the baking aisle at the grocery store, but if you’re coming up empty handed, you can make a close approximation at home. Place regular granulated sugar in a food processor and blend until fine.
Coat three 9-inch baking pans with vegetable shortening or flour-based baking spray (I like Baker’s Joy) and line the bottoms of the pans with parchment paper.
Mix the flour, baking powder and salt in a large bowl.
Beat the butter, oil and granulated sugar together in a separate large bowl until light and fluffy. Add egg whites one at a time, beating well after each addition.
Beat in the flour and buttermilk alternately with the mixer on low speed; begin and end with the flour. Scrape down the bowl as needed. Gently fold in the mini chocolate chips.
Divide the batter evenly between the prepared pans. Bake for 35 to 40 minutes, or until the cakes spring back when pressed in the centers. Allow the cakes to cool in the pans for 10 minutes, and then turn out onto wire cooling racks to cool completely. Level the tops of the cooled cakes with a large serrated knife or a cake leveler.
Make the sweet cream syrup:
In a saucepan combine the sugar and cream. Cook over medium heat until the mixture is steaming but not boiling and the sugar is melted. Remove from the heat and let cool. Add the vanilla. Use this syrup to brush the cake layers for extra moisture.
Make the filling:
Beat the brown sugar and butter together in a bowl with an electric mixer until fluffy. Beat in the vanilla extract. Add the flour and salt and mix until combined. Add cream a little at a time until the mixture is spreading consistency (you may not have to use all of the cream). Fold in chocolate chips. Place a cake layer on a serving plate or cake stand. Cover the layer with half of the cookie dough frosting and top with a second cake layer. Cover the second layer with the remaining frosting. Place the remaining cake layer on top.
Make the frosting:
In a medium saucepan, whisk together flour and 1/2 cup of milk until smooth. Set over medium-high heat and let cook for 3 minutes, or until slightly hot. Whisk in remaining milk and salt. Whisk constantly until the mixture has thickened to the consistency of unset pudding (this can take up to 10 minutes). Remove from heat and pour the mixture into a shallow dish. Place in the refrigerator until cool. When cool, mixture will be thick like custard.
In a large bowl (or bowl of a stand mixer, if you have one) beat the butter and sugar together until fluffy. Add vanilla and mix well. Beat in cooled flour mixture one tablespoon at a time on medium-high speed. When all the flour mixture is added beat on high speed until light and fluffy, about 6 minutes. Rub a little frosting between your fingers, if sugar granules remain, beat for 4 more minutes, or until granules cannot be detected with fingers.
Frost the entire cake with the milk frosting in an even layer; transfer leftover frosting to a piping bag fitted with an open star tip and pipe swirls or stars around the top edge of the cake. Use regular-size chocolate chips to decorate the outside of the cake. Place chips in staggered lines around the outside edge, beginning at the top and working your way down. Decorate the top edge of the cake with the mini chips.
Serve cake slices at room temperature. Store the cake covered in the refrigerator; bring to room temperature before serving
Keyword boiled frosting, chocolate chip cookie dough filling, mini chocolate chips, sweet cream syrup, white cake mix