Preheat oven to 350 degrees F. Line a 9x13 inch baking pan with foil or parchment paper and spray with non-stick cooking spray.
Melt butter, the combine in a large bowl with brown sugar and stir very well to combine. Add in salt and vanilla and stir to combine.
Add eggs, one at a time, mixing well after each addition. Mix until well combined.
Add flour, baking powder and chocolate chips. Stir until combined, but do not overmix.
Spread batter into prepared pan and smooth to cover the entire bottom of pan. Bake for 28-33 minutes, until they have risen and their tops are shiny and golden. They may not seem as if they are completely baked through, and a toothpick inserted into the center will NOT come out clean - if it does they are over baked. Remove from oven and allow to cool, in pan, on a wire rack for at least an hour prior to slicing. Wrap tightly to maintain chewy texture.