Measure 3 cups flour, and add baking powder, baking soda, and salt. Stir the brown sugar into the melted butter and mix well. Mix the beaten egg and vanilla into the brown sugar mixture. Add flour mixture, a little at a time, mixing just until combined, then stir in the chocolate chips, minus the 1/2 cup for the top.
Spread the batter into the prepared pan and top with the remaining chocolate chips. Bake in the preheated oven until a toothpick inserted in the center comes out clean, about 25 to 30 minutes.