Preheat the oven to 350°F (175°C) and grease an 8x8 inch baking pan.
In a large bowl, mix the melted butter and sugar until smooth.
Add the eggs one at a time and beat well after each addition. Stir in the vanilla extract.
Sift together the cocoa powder, flour, salt, and baking powder. Gradually stir into the butter mixture until well blended.
Fold in chocolate chips, if using. Spread the batter evenly into the prepared baking pan.
Bake for 25 to 30 minutes in the preheated oven, until the brownies begin to pull away from the sides of the pan. Let cool in pan before cutting into squares.
Notes
For an extra fudgy texture, bake closer to 25 minutes. Store leftovers in an airtight container for up to three days.