In a large mixing bowl, cream the softened butter and granulated sugar together until light and fluffy (about 2-3 minutes).

Beat in the egg and vanilla extract until combined.

In a separate bowl, whisk together the all-purpose flour, cocoa powder, and salt. Gradually add this dry mixture to the butter mixture, beating until just combined.

Transfer the dough to the refrigerator to chill for at least 1 hour.

Heat the whipping cream in the microwave until it simmers (about 1.5 minutes on high).

Pour the warm cream over the chopped semisweet chocolate and whisk until smooth. Cool it in the refrigerator until spreadable (about 30 minutes).

Preheat your oven to 350°F (175°C).

Roll out half the dough to about 1/4 inch thickness between two sheets of parchment paper. Use a 2-inch cookie cutter to cut out shapes.

Place the shaped cookies on a baking sheet lined with parchment.

Bake for 9 to 11 minutes, or until firm. Let them cool for about 2 minutes before transferring to a wire rack to cool completely.

Once cooled, take half of the cookies and spread about 2 teaspoons of the ganache filling on the flat side, topping them with the remaining cookies.