For best success, I recommend reviewing the recipe notes and video tutorial above before beginning.

Preheat the oven to 350°F (177°C) and line a 9-inch square baking pan with parchment paper, leaving enough overhang on the sides to lift the warm brownies out. Set aside. (If you have 2 identical 9-inch square baking pans, you can line both and bake the batches of brownie batter at the same time.) I don’t recommend other size baking pans. See my recipe note.

In a microwave-safe bowl or a saucepan on the stove, melt the butter. After melting, whisk in the sugar until completely combined, then whisk in the eggs and vanilla. The batter will be a little dull looking.

Add the cocoa powder, flour, salt, and baking powder. Fold it all together with a rubber spatula or wooden spoon. It will come together, I promise! Batter will be very thick. You will have about 4 cups of batter.

Spoon and spread half of the batter (about 2 cups) into prepared pan. (Lightly cover remaining batter and keep at room temperature.) The batter is thick and heavy, so do your best to spread it evenly in the lined baking pan. I find the back of a spoon is most helpful. Place a small sheet of parchment paper directly on top of the brownie batter, smoothing it down as pictured in the photos and video tutorial above. The top parchment paper helps the brownies stay flat and prevents the brownies from puffing up too much.

Bake for 15-16 minutes. I find any longer over-cooks the brownies, making the ice cream sandwiches difficult to cut and eat. Remove brownies from the oven and cool for 5 minutes in the pan. Carefully, using the overhanging parchment paper on the sides, lift the warm and soft square sheet of brownies out of the pan as a whole. Remove top piece of parchment. (You can reuse it for the top of the 2nd sheet of brownies in the next step, if desired.) Set aside.

Line the warm pan with another sheet of parchment paper, leaving enough overhang on the sides to lift the warm brownies out. Give the remaining brownie batter a stir. It will be very thick at this point. Add a teaspoon of water to thin out if necessary. (No more.) Spoon and spread the remaining brownie batter in the pan. Place a small sheet of parchment paper directly on top of the brownie batter, just as you did before.

Bake for 15-16 minutes. Remove brownies from the oven and cool for 15 minutes in the pan. During this cooling time, I remove the ice cream from the freezer so it has a chance to soften.

Scoop the softened ice cream onto the warm brownie layer in the pan. You’ll use almost all of the 1/2 gallon of ice cream. Using the back of a spoon or your ice cream scoop, gently spread it into an even and thick layer.

Carefully pick up the 1st square sheet of brownies and place on top of the ice cream layer. Gently press it down into the ice cream to help it stick. Cover the entire pan with aluminum foil or plastic wrap and freeze for at least 12 hours and up to 1 week. I find 12-18 hours is the perfect amount of time. Any less and the ice cream will still be pretty soft. The longer after 18 hours, the harder the sandwiches are to cut.

Remove the pan of ice cream brownies from the freezer. Carefully lift them out as a whole using the parchment paper overhang on the sides. Using a very sharp knife and some arm muscle, cut into 8-12 squares or rectangles. Enjoy immediately.

Wrap each leftover sandwich individually and store in the freezer for up to 1 month. They get a little harder the longer they sit in the freezer—if they’re super solid, let them sit out for a few minutes before enjoying.