Make the Cookie Bases

1. Preheat the oven to 375°F (190°C). Prepare two 9×13 inch baking pans with parchment paper in the bottom and spray the sides.
2. In a medium sized bowl, combine the flour, cocoa, baking powder and salt. Set aside.
3. Beat the butter and sugar just until combined and smooth.
4. Add the egg and milk and mix until well combined.
5. Add the flour mixture and mix just until well combined.
6. Divide the batter evenly between the two cake pans. I used a food scale to do that accurately, but you could measure with cups as well. Spread the batter evenly. It’ll be very thin. Bake for 5-8 minutes or until a toothpick comes out clean.
7. Allow to cool mostly in the pan, then turn out onto a cooling rack that’s large enough for the full cake. You’ll want to line the cooling rack with parchment paper and lightly spray the parchment with non-stick baking spray, so that it doesn’t stick. The “tops” of the cakes will end up being the outside of the ice cream sandwiches and ideally they’ll look nice, so you don’t want them to stick to the parchment paper.

Build the Ice Cream Sandwiches

1. Prior to building the ice cream sandwiches, put the cakes into the freezer for about 20-30 minutes (you can freeze them for longer if you want to do that ahead of time). Set the first flavor of ice cream (I used vanilla first) out for about 15-20 minutes prior to using, as well.
2. Prepare one of the 9×13-inch baking pans for building the sandwiches. Be sure it’s clean and line it with parchment paper that sticks above the two long sides of the pan. You’ll use those for lifting the bars out of the pan for later. Add one of the frozen cakes to the bottom of the pan with the “pretty side” (or the top of the cake) on the bottom/facing down.
3. Add about half of the ice cream flavor you’re using first to a large bowl and stir well until smooth and spreadable. Spread into an even layer on top of the chocolate cake layer. Set the pan back into the freezer for 30 minutes to an hour, depending on your freezer. You want the ice cream firm enough that it won’t move around when you add the next layer.
4. About 15-20 minutes before adding the second ice cream flavor, set it out to thaw a bit. Then add about half of the ice cream flavor you’re using second to a large bowl and stir well until smooth and spreadable. Spread into an even layer on top of the previous ice cream layer.
5. Add the second frozen chocolate cake on top of the ice cream, with the “pretty side” up. Press it lightly onto the ice cream so it sticks well and fills in any gaps. Freeze again until firm and frozen, at least 2 hours.
6. Use the parchment paper to lift the sandwiches out of the pan. Cut off the rough edges with a long knife, then cut into bars.
7. Store in the freezer until ready to serve.