Preheat the oven to 350F, and line a 10x10 baking pan with parchment paper.

In a large bowl, whisk together the ground flaxseed and water, and let sit for 5 minutes to thicken.

Whisk in the sugar, melted butter, sugar, cocoa, baking soda, salt, nondairy milk, and melted chocolate until combined. Finally, stir in the flour. Batter will be thick!

Pour into prepared pan and bake for 35-40 minutes, until a toothpick inserted in the center comes out with just a few moist crumbs. Allow to cool completely before assembling.

When almost ready to assemble, take your ice cream out of the freezer and let sit at room temperature for about 10 minutes to soften. When brownie is completely cooled, remove from the pan. Carefully cut it in half to create two thin brownie layers, and replace the bottom layer with the parchment paper back in the pan.

Scoop ice cream as desired on the bottom half of the brownie to create desired flavors, and spread using a spoon or offset spatula. If you are making 3 different flavors, you will not use the whole pint! When done, replace the top layer of brownie on top of the ice cream, and place brownie in the freezer. Allow to chill until frozen solid, at least 3-4 hours.

Now, you can cut the brownie ice cream sandwiches! Lift the parchment paper out of the pan, and cut brownie sandwiches as desired (I cut it into 12 to make 4 sandwiches for each flavor). Enjoy immediately or store in freezer until needed!