Preheat oven to 325 degrees. Line two baking sheets with parchment paper. In a large bowl, whisk together sugar, cocoa powder, almond flour, potato starch, cinnamon, and salt. Using a hand-held mixer at medium speed, mix in the egg whites one at time. Add the vanilla, increase speed to high, and beat for 3 minutes, scraping down the sides of the bowl a couple of times. Stir in the pecans and chocolate.
Drop tablespoonfuls of batter on the prepared baking sheets at 1½- to 2-inch intervals. Bake 15 to 17 minutes, rotating the pans halfway through, until the cookies look shiny and slightly crackled and the edges seem dry. Remove from oven and let cookies rest on the pans for 2 to 3 minutes before sliding the parchment sheets onto wire racks. Let the cookies cool completely before peeling them from the paper. Store between sheets of wax paper in an airtight container (the cookies will stick together if stacked directly on top of each other).
To make the sandwiches, soften the ice cream by putting it in the refrigerator about 20 to 30 minutes or by heating it for 5 seconds at a time in the microwave. It will need to be soft enough to spread on the cookies without breaking them. Gently spread about 2 to 3 tablespoons of ice cream on the bottom of one cookie and top with another cookie, squeezing the sandwich lightly together. If not eating right away, place the sandwiches on a wax-paper-lined tray and freeze until solid, then wrap them individually in wax paper and place in a sealed bag. Allow them to soften slightly (about 5 minutes) at room temperature before serving.