Preheat oven to 350 degrees. Butter or spray an 8x8-inch baking dish with nonstick spray then line with parchment paper allowing a 2" overhang. Spray parchment paper.
In a small saucepan, heat butter and both sugars over medium heat. Cook until the mixture comes to a boil and has thickened, about 5 minutes. Remove from heat and stir in vanilla and nuts, if adding. Let cool slightly. Once cool, whisk in egg.
In a medium bowl, combine flour and baking powder. Add sugar mixture and until just incorporated.
Stir in chips. Pour into prepared pan and level with fingers.
Bake for 30-35 minutes or until toothpick inserted in center comes out clean. Let cool on wire rack.