Preheat oven to 350 degrees F, dump the dry cake mix onto an unlined rimmed baking sheet, then bake in preheated oven for 5 minutes or until the cake mix has reached 160 degrees F**.
Carefully place the heat treated cake mix into a large bowl, then whisk in buttermilk, canola oil, and sour cream until combined.
Remove 1 cup of the batter and set aside.
Pour the remaining batter into a greased 9x13 inch glass baking dish and bake for 30 minutes at 350 degrees F or until the cake has baked through.
Allow to cool for 10 minutes at room temperature, before placing the cake in the fridge to finish cooling. Once the cake has cooled, cube the cake into large chunks and measure out 2 heaping cups***. Set aside.
Pour the heavy cream into the bowl of your stand mixer**** and whip until stiff peaks form.
While whipping continually, slowly drizzle in the remaining 1 cup batter and the sweetened condensed milk.
Use a rubber spatula to gently fold in the cake pieces, then pour half of the mixture into a large freezer safe airtight Tupperware container.
Swirl in half the can of frosting, top with the remaining ice cream mixture, then swirl in the remaining frosting.
Cover and freeze overnight, then scoop and enjoy!
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