Prepare your workspace by lining two baking sheets with parchment paper and taking your ice cream out of the freezer to soften slightly (about 10 minutes).
In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt until well combined and no cocoa lumps remain.
Using an electric mixer, cream the butter and sugar together in a large bowl until light and fluffy, about 2-3 minutes. This incorporation of air is crucial for the right cookie texture.
Add the egg and vanilla to the butter mixture and beat until fully incorporated, scraping down the sides of the bowl as needed.
Gradually add the dry ingredients to the wet ingredients, mixing on low speed just until combined. Overmixing will result in tough cookies.
Cover the dough and refrigerate for at least 30 minutes. This prevents excessive spreading during baking.
Preheat your oven to 350°F (175°C) while the dough is chilling.
Using a cookie scoop or tablespoon, portion the dough into 24 equal balls and place them on the prepared baking sheets, spacing them about 2 inches apart.
Gently flatten each cookie with the bottom of a glass or measuring cup to about 1/4-inch thickness. For perfectly shaped sandwiches, use a round cookie cutter as a guide.
Bake for 8-10 minutes until the edges are set but the centers still appear slightly soft. They should not be crispy!
Cool completely on the baking sheets for 5 minutes, then transfer to wire racks to finish cooling.
Once cookies are completely cooled, scoop slightly softened ice cream onto the flat side of one cookie, then top with another cookie, flat side down, and gently press to create a sandwich.
Immediately wrap each sandwich in plastic wrap and place in the freezer. If adding edge toppings, roll the exposed ice cream edges in your chosen topping before freezing.
Freeze for at least 2 hours or until the ice cream is firm again.