Preheat the oven to 350°F (175°C).

Mix the dry ingredients in a bowl by combining the all-purpose flour, baking soda, and salt.

Cream the softened butter with granulated sugar and light brown sugar in another bowl until light and fluffy.

Add the egg, instant coffee granules, and vanilla extract to the butter mixture, mixing until well combined.

Gradually incorporate the dry ingredients into the wet mixture until just combined.

Fold in the unsweetened cocoa powder.

Drop spoonfuls of dough onto a parchment-lined baking sheet and flatten them slightly.

Bake for 12 minutes or until the edges are set but the centers still appear soft.

Prepare the filling while the cookies bake by mixing the mascarpone cheese, powdered sugar, vanilla extract, and heavy cream until smooth.

Spread the filling on the flat side of one cooled cookie and press another cookie on top to create a sandwich.

Optional: Dust with extra cocoa powder before serving.