Preheat your oven to 350°F (175°C) and prepare a 9x13-inch baking pan.
In a bowl, whisk together flour, cocoa powder, salt, and baking powder.
Melt the butter and mix with granulated and brown sugar until smooth. Add eggs one at a time, then stir in vanilla.
Gradually add dry ingredients to wet mixture, stirring gently until just combined.
Pour batter into the prepared pan and drop spoonfuls of cookie dough on top, pressing gently.
Bake for 25-30 minutes, checking for doneness with a toothpick.
Let cool for at least 15 minutes before cutting into squares and serving.