Heat oven to 350°F. Line a 9x13-inch pan with parchment and lightly grease.
Whisk flour, baking powder, and salt in a medium bowl; set aside.
Stir melted butter, brown sugar, and granulated sugar in a large bowl until glossy and smooth.
Beat in eggs one at a time, then mix in vanilla until fully combined.
Fold dry ingredients into the wet mixture just until no dry spots remain. Do not overmix.
Stir in chocolate chips and nuts to evenly distribute.
Scrape batter into the prepared pan and smooth the top.
Bake 26–30 minutes, until the top is golden and a toothpick comes out with a few moist crumbs.
Cool completely in the pan on a rack. Lift out using parchment and cut into bars.