Preheat the oven to 350 degrees F (175 degrees C). Grease an 8 inch square baking dish.
In a large bowl, combine the flour, cocoa, baking powder and salt; set aside. In a separate bowl, stir together the melted butter, sugar, and vanilla. Mix in the eggs. Gradually stir in the dry ingredients just until blended. Fold in chocolate chips and pecans if using. Spread the batter evenly in the prepared pan.
Bake in the preheated oven until the edges start to pull away from the sides of the pan and the top appears dry, 35 to 40 minutes.
