- Brownie box mix (plus egg, oil, and water to make it) or homemade recipe designed for an 8-inch pan
- 15 ounces (or a little over 3 cups) vanilla, mint chocolate chip, or favorite ice cream flavor (about ½ a 1.44 quart container – you can eyeball)
Preheat the oven to 350℉. Line two 8-inch square baking pans or a 13×9 metal baking pan with parchment paper, creasing well at the edges and corners and leaving enough overhang on the sides to lift the brownies out when cooked.
In a mixing bowl, prepare the brownies according to the box or recipe directions.
Transfer the batter to the prepared pan(s), smoothing it into an even layer with a rubber spatula or the back of a standard spoon. (If using two 8-inch pans, add half the batter to each pan. If you only have one 8-inch pan, you may bake in 2 batches. Just take care to make them even.)
Bake for 14-16 minutes or until set in the middle. (Tip: Many people like to undercook brownies, but for ease of working with and best texture once frozen, you want these to be fully cooked – yet not too firm around the edges, which can make the sandwiches difficult to cut and eat.) Remove the brownies from the oven and cool on a rack for 10 minutes in the pan. Freeze the brownies in pan, uncovered, until completely cool, at least 20 minutes or up to 1 hour. You could freezer longer but cover after an hour or so. Freezing the brownies now simply makes them less pliable/more sturdy to work with and prevents the ice cream from melting as quickly during assembly.
Once chilled, lift the brownies out of the pan. Remove the parchment, but for easier transfer later, keep a sheet of parchment under the brownie during assembly. If you used the 9×13 pan, cut the brownie in half so you have two squares.
Meanwhile, just before removing the brownies from the freezer, remove the ice cream from the freezer to soften. Depending on freezer and room temperature, this usually takes 5-10 minutes.
Place one brownie square (good side down) on another piece of parchment, cardboard, a cutting board, or back in the baking pan (this will make transfer back to the freezer easier) and scoop the softened ice cream onto the brownie. Using a spatula or back or a spoon, quickly spread it into a thick and even layer.
Carefully place the other piece of brownie on top of the ice cream, good side up, making sure the edges line up. Gently press it into the ice cream to help it stick.
Return to the freezer, making sure it sits flat, cover with aluminum foil or plastic wrap, and freeze for at least 6 hours – overnight is best – and up to 1 week. Pro tip: If you’d like really clean edges, when firm, soften a little extra ice cream and fill in any gaps along the sides.
Once firm, place the brownie on a cutting board and, with a long, sharp knife, cut into 10 bars, 9 squares, or whatever your desired bar size may be. Tips: For clean cuts, it’s helpful to rinse the knife in hot water—and quickly dry—in between cuts. Also, remember that you can put the bars back in the freezer if at any point the ice cream becomes too soft.
Enjoy immediately or wrap each sandwich individually and return to the freezer.
Storage: Wrap each sandwich individually in parchment paper, wax paper, or plastic wrap, and then store in a zip-top bag or airtight container in the freezer for up to 1 month. They will likely keep longer if they are well wrapped and stored in the bottom/back of the freezer, where the temperature tends to stay constant and discourage freezer burn. If they’re frozen hard, let the sandwiches sit at room temperature for a few minutes before enjoying.
For a hint of salty-sweetness, very lightly but evenly sprinkle the surface of the brownies with flaky sea salt before baking.
Helpful hint: Once assembled, give the brownies sufficient time to freeze. That way, they will slice into neat rectangles or squares and the ice cream won’t ooze out when cutting.
Ice cream details: Premium ice creams with a higher butter fat level will freeze harder, so I recommend a grocery store brand like Turkey Hill or Edy’s. Non-dairy ice cream may certainly be used.
For a gluten-free dessert, I use my homemade brownies (the base recipe without the Halloween candy option in the linked recipe; a handful of chocolate chips mixed into the batter is fair game though) and use a cup-for-cup gluten-free flour like King Arthur Flour’s Measure for Measure.
When using a store-bought brownie mix, I typically use Ghirardelli brand although all the major brands will work well. For proper thickness, just be sure to use the 8×8 size.