Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, and salt. Set aside.
In a large mixing bowl, combine the melted butter, granulated sugar, and brown sugar until smooth.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract until combined.
Gradually add the dry mixture into the wet mixture, stirring until just combined. Be careful not to overmix.
Fold in the chocolate chips and chopped nuts if using, ensuring they are evenly distributed in the dough.
Scoop tablespoons of cookie dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are set but the centers are still slightly soft.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Notes
Arrange the cookies on a decorative plate, and sprinkle a little sea salt on top for a contrast in flavors. These cookies pair wonderfully with a glass of milk or a scoop of vanilla ice cream!