DOUBLE CHOCOLATE MOCHA SANDWICH COOKIES

1. Preheat oven to 350°F and line a baking sheet with parchment paper.
2. Melt the butter and allow it to cool until it is only warm to the touch.
3. Whisk the cocoa powder into the butter until smooth and glossy.
4. Add the brown sugar, granulated sugar, egg, and vanilla. Mix until well combined.
5. Add the flour, baking soda, and salt. Stir just until a soft dough forms.
6. Scoop tablespoon-sized portions onto the prepared baking sheet.
7. Bake for 8-10 minutes, until the edges are set and the centers are still slightly soft.
8. For a flatter, bakery-style cookie, gently drop the baking sheet on the counter once or twice immediately after removing it from the oven.
9. Let cool on the baking sheet for 5 minutes before transferring to a wire rack.
10. Make sure the cookies are completely cool before adding the filling.

For the filling, beat the butter until creamy. Add the powdered sugar, cocoa powder, espresso powder, vanilla, and salt. Mix until smooth, adding milk or cream as needed.

To assemble, spread or pipe filling onto half the cookies and top with the remaining cookies.