Preheat oven to 350°F. Prepare three 8-inch cake pans with parchment paper and greased sides. Cream together butter and sugars until fluffy. Add sour cream and vanilla, mix well. Add eggs one at a time. In a separate bowl, combine dry ingredients. Mix dry and wet ingredients alternately with milk and water, then fold in mini chocolate chips. Divide batter into prepared pans and bake for 21-23 minutes. Cool completely.

Prepare frosting: Beat butter and shortening until smooth. Gradually add powdered sugar, vanilla, and water/milk until desired consistency is reached.

Assemble cake: Level cakes if necessary, spread frosting between layers, crumble cookies with milk and spread over each layer inside the dam, then frost the outside of the cake. Decorate with mini chocolate chips as desired.