Prepare the Cookie Dough : In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 2–3 minutes. Beat in the egg, vanilla extract, and almond milk until fully combined.

Combine Dry Ingredients : In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking soda, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix.

Add the Marshmallows : Gently fold the mini marshmallows into the cookie dough until evenly distributed.

Chill the Dough : Cover the bowl with plastic wrap and refrigerate the dough for at least 30 minutes. Chilling prevents the cookies from spreading too much while baking.

Bake the Cookies : Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Scoop about 1 ½ tablespoons of dough for each cookie and roll into balls. Place the dough balls on the prepared baking sheets, spacing them about 2 inches apart. Bake for 9–10 minutes, or until the edges are set but the centers are still soft. The marshmallows may melt slightly, creating a gooey texture.

Cool the Cookies : Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

Serve and Enjoy : Serve the cookies warm for the ultimate gooey marshmallow experience, or store them in an airtight container at room temperature for up to 3 days.