Preheat the oven to 325 degrees F (165 degrees C). Grease a 9x13 inch baking pan.

Combine brown sugar and melted butter in a large bowl; cool slightly. Beat in eggs, one at a time.

Combine flour, baking powder, and salt in a separate bowl. Add to brown sugar mixture; mix well. Stir in walnuts and chocolate chips. Pour into the prepared baking pan.

Bake in the preheated oven for 25 to 30 minutes. When almost cool, cut into 48 squares.