Preheat your oven to 350°F (175°C).

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

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

Beat in the egg and vanilla extract until well combined.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Scoop out dough and roll into balls, placing them on a baking sheet spaced about 2 inches apart.

Make an indentation in the center of each dough ball using your thumb.

Bake for 10-12 minutes until edges are set but centers are soft.

Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack.

Fill each thumbprint with about 1 teaspoon of chocolate hazelnut spread.