Start by preheating your oven to 350°F (175°C).
In a medium bowl, whisk together the flour, salt, baking powder, and baking soda.
In a large mixing bowl, use an electric mixer or whisk to cream the room temperature butter and sugar together until light and fluffy.
Next, sift the cocoa powder into the butter-sugar mixture and mix until well combined. Then, add the eggs one at a time, beating well after each addition, along with the vanilla extract.
Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.
Finally, fold in the melted semisweet chocolate until evenly distributed.
Using a cookie scoop or tablespoon, drop rounded tablespoons of dough onto a lined baking sheet, creating an indent in the center of each cookie.
Bake for 10-12 minutes or until the edges are set.
Remove from the oven, cool for 5 minutes, then transfer to a wire rack and fill the thumbprints with your favorite filling.