Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a mixing bowl, combine the melted butter and granulated sugar. Stir until well combined and smooth.
Add the eggs, one at a time, mixing well after each addition, then stir in the vanilla extract.
In another bowl, whisk together the flour, cocoa powder, baking powder, and salt. Gradually add this dry mixture to the wet mixture, stirring just until combined.
Fold in the chocolate chips and nuts (if using) until evenly distributed throughout the dough.
Using a cookie scoop or tablespoon, drop dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 10-12 minutes, or until the edges are set and the centers look slightly soft.
Remove from the oven and let the cookies cool on the baking sheet for about 5 minutes before transferring them to a wire rack to cool completely.