Preheat your oven to 350°F. Line two baking sheets with parchment paper.

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

Beat in the egg and vanilla extract until well combined.

In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking powder, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until a dough forms.

On a lightly floured surface, roll out the dough to about 1/8-inch thickness.

Use a round cookie cutter to cut out circles and place them on the prepared baking sheets.

Bake for 8 to 10 minutes, until the edges are set. Let the cookies cool completely.

In a bowl, beat together the softened butter and vegetable shortening until smooth.

Spread or pipe a small amount of filling onto the flat side of a cookie.

Place another cookie on top, pressing gently to spread the filling to the edges.

Repeat with the remaining cookies and filling.