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

In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

In another bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, mixing until a dough forms.

Divide the dough into two equal portions and roll each portion into a log about 1 inch in diameter. Wrap the logs in plastic wrap and refrigerate for at least 30 minutes.

Once chilled, remove the logs from the refrigerator and slice them into 1/4-inch thick rounds. Place the rounds on the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes, or until the edges are firm. Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

Once cooled, spread a small amount of chocolate chips between two cookies to create a sandwich. Dust the finished cookies with powdered sugar before serving.