Prepare two 8-inch springform or cake pans with a parchment paper circle in the bottom and grease the sides. Preheat oven to 350°F.

In a large mixing bowl, cream the butter and sugars together until light in color and fluffy, about 3-4 minutes. Do not skimp on the creaming time.

Add sour cream and vanilla extract and mix until well-combined.

Add egg whites in two batches, mixing until well combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.

Combine dry ingredients in a separate bowl, then combine the milk and water in a small measuring cup.

Add half of the dry ingredients to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.

Pour the batter evenly into the cake pan and bake for about 18-20 minutes, or until a toothpick comes out with a few crumbs.

Remove the cake from the oven and allow to cool for about 2-3 minutes, then remove to a cooling rack to cool completely.

In a large mixer bowl, combine the cream cheese and brown sugar and mix until smooth.

Add the milk, vanilla extract and cinnamon and milk until well combined and smooth. Set aside.

In another mixer bowl, add the heavy whipping cream and powdered sugar and whip on high speed until stiff peaks form.

Gently fold the whipped cream into the cream cheese mixture until well combined.

Gently fold in the mini chocolate chips and oatmeal cookie pieces until combined throughout.

Line the sides of an 8-inch springform pan with parchment paper. The parchment paper should stick up above the top edge of the pan, since the cake will probably be a little taller than your pan (see example). If you want to, put a cardboard cake circle in the bottom of the pan. If not using a springform pan, you pan put some plastic wrap in the bottom of the pan and up the sides and use it to lift the cake out of the pan when it’s done. If using a clear cake collar, wrap it around the bottom layer of the cake and secure in place with tape. Note: You should be using the same 8-inch pan you used for the cake. Not all 8-inch pans are exactly the same size. Your cake needs to fit in this pan.

Cut the dome off the tops of the cake layers. Place the first cake layer into the bottom of the pan.

Spread half of the ice cream mixture evenly over the cake layer.

Top the ice cream with the other layer of cake, then add the remaining ice cream.

Freeze cake until firm, 6-8 hours or overnight. Once frozen, remove from springform pan and remove parchment paper from sides, or remove the clear cake collar.

To make the whipped cream frosting, whip the heavy whipping cream, powdered sugar, brown sugar and vanilla extract on high speed until stiff peaks form.

Frost the outside of the cake with the whipped cream, then pipe swirls around the top edge.

To finish off the cake, press mini chocolate chips onto the sides of the cake and top it with oatmeal chocolate chip cookies, if desired.

Freeze the cake until ready to serve. Allow to thaw for 45 minutes to an hour before serving.