Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, salt, baking powder, baking soda, and cocoa powder.
In a large mixing bowl, beat the room temperature butter and sugar together until light and fluffy.
Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract and melted chocolate.
Gradually add the dry mixture to the wet ingredients, mixing until just combined.
Using a cookie scoop, drop tablespoon-sized balls of dough onto the prepared baking sheet and press your thumb into the center of each dough ball.
Bake in the preheated oven for 10-12 minutes until soft but set around the edges.
Remove the cookies from the oven and press the thumbprint center again if it has puffed up, then let them cool on the baking sheet.
Once cooled, fill each thumbprint with your favorite chocolate ganache or jam.
