Preheat the oven to 350°F (175°C) and line two baking sheets with parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt.
In a large bowl, beat the butter and sugar until light and fluffy, about 2 to 3 minutes.
Beat in the egg, red food coloring, and vanilla extract until combined.
Add the dry ingredients in two additions, alternating with the buttermilk, mixing just until combined.
Scoop the dough into 16 equal portions and place on the prepared baking sheets, spacing them a few inches apart. Flatten slightly with your hand or the bottom of a glass.
Bake for 10 to 12 minutes, until the edges are set and the centers look slightly soft. Cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.
Once cooled, pair the cookies by size. Place a scoop of vanilla ice cream on the flat side of one cookie, top with a second cookie, and gently press together.
If desired, roll the ice cream edges in mini chocolate chips or sprinkles. Freeze the sandwiches for at least 1 hour before serving.