01 - Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper to prevent sticking.
02 - In a mixing bowl, whisk together the all-purpose flour, unsweetened cocoa powder, baking soda, and salt.
03 - In a separate large bowl, use an electric mixer or whisk to cream the softened unsalted butter and granulated sugar until the mixture is light and fluffy.
04 - Beat the egg and vanilla extract into the creamed butter and sugar mixture until well combined.
05 - Gradually add the dry ingredients to the wet ingredients, mixing until just combined to form a cohesive dough.
06 - Portion the dough into 16 evenly sized balls. Place them approximately 2 inches apart on the prepared baking sheets. Gently flatten each ball slightly with your hand or the bottom of a glass. Bake for 10-12 minutes, or until the cookie edges are firm and set.
07 - Allow the baked cookies to cool completely on a wire rack.
08 - In a large bowl, whisk together the heavy cream, whole milk, granulated sugar, salt, root beer extract, and vanilla extract until the sugar is fully dissolved.
09 - Churn the ice cream base in an ice cream maker according to the manufacturer's instructions until it reaches a soft-serve consistency. Transfer the churned ice cream to a freezer-safe container and freeze for at least 2 hours, or until firm.
10 - To assemble the ice cream sandwiches, place a scoop of the frozen root beer ice cream on the flat side of one cookie. Top with a second cookie and gently press to form a sandwich. Repeat this process with the remaining cookies and ice cream.
11 - Wrap each assembled ice cream sandwich individually in parchment paper. Freeze for an additional 30 minutes before serving to achieve the best texture.