Add the butter and semi-sweet chocolate chips to a medium saucepan and melt over medium heat, stirring frequently until melted and mixed well.
Remove the pan from the heat and allow to rest until cool for 10 - 15 minutes.
In a large mixing bowl, add the flour, cocoa powder, baking powder, baking soda, and salt and whisk together to combine. Then set the bowl with the dry ingredients aside.
In the bowl of a stand mixer, add the light-brown sugar, granulated sugar, eggs, and vanilla and whip together with the paddle attachment on medium-high speed until pale and fluffy, which will take about 1 minute.
Using a rubber spatula stir the melted chocolate mixture into the sugar and egg mixture.
Working in 3 separate batches, add 1/3 of the flour mixture to the wet ingredients and fold just until combined.
Chill the bowl of cookie dough in the fridge for 45 minutes.
Preheat the oven to 325°F degrees during the last 10 minutes of chilling.
Scoop a tablespoon of the dough out and shape it into balls.
Place onto Silpat or parchment paper lined cookie sheets, spacing them 2 inches apart.
Bake the cookies in preheated oven 12 - 13 minutes, then remove from oven and allow to cool on baking sheet 5 minutes before transferring to a wire rack to cool completely.