Preheat oven to 150 degrees F. Line 2 6-inch (or 3 4-inch and a loaf pan, like I used) springform or cake pans with parchment paper and set aside.
Combine brownie mix, eggs, coconut oil, coffee, and vanilla in a medium bowl. Mix on medium speed until combined - expect a few small lumps.
Portion batter into prepared cake pans and bake for 20-35 minutes, depending on pan size. When a toothpick inserted in the center comes out clean, it's done.
Allow to cool mostly in pans, then remove to cooling rack to cool completely before continuing.
When ready to assemble, take ice cream out of the freezer about 10 minutes before beginning work, and allow it to soften a bit.
Return brownie to (freshly-lined with parchment) pan, then top with an even layer ice cream, to help mold the shape of the cake. Fill it with as much ice cream as you like - I usually fill mine to the top.
Cover with plastic wrap and return to freezer to freeze completely, 6-8 hours.
Caramel Mocha Whipped Cream
Place all ingredients in the chilled bowl of a stand mixer fitted with a whisk attachment. Whisk for 1-2 minutes on low to incorporate, then increase speed to medium-high until firm peaks form, another 6-8 minutes. Be sure not to overwhip, unless you are looking to make caramel mocha butter!
When ready to decorate, be ready to move quickly; take cake base out of freezer and carefully remove it from the pan, placing it on a cake plate. Firmly press the second brownie on top, and ice with Caramel Mocha Whipped Cream. Drizzle caramel sauce along the top edge, allowing it to drip down the sides. Garnish with any extra brownie pieces.
Notes
To make a larger cake, double the brownie recipe and amount of ice cream to 4 cups.