Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.

Whisk together flour, cocoa powder, baking soda, and salt in a medium bowl, then set aside.

In a large bowl, cream together softened butter, granulated sugar, and brown sugar until light and fluffy using an electric mixer.

Beat in the egg and vanilla extract until well combined.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined and a soft dough forms.

Drop rounded tablespoons of dough onto the prepared baking sheets, leaving space between them.

Bake for 10-12 minutes, or until the edges are set and the centers are still slightly soft; let them cool on the sheets for a few minutes before transferring to a wire rack to cool completely.

Once the cookies are completely cool, scoop about a quarter cup of slightly softened ice cream onto the flat side of half of the cookies.

Top each with another cookie, gently pressing down to spread the ice cream to the edges.

If desired, roll the edges of the sandwiches in sprinkles or mini chocolate chips.

Wrap each ice cream sandwich individually in plastic wrap or parchment paper and freeze for at least 2 hours, or until firm, before serving.