Brown the butter by placing it in a medium saucepan over low heat to cook until medium-brown (not too light, not too burned), about 10 minutes. Remove from the heat and let it cool.
Preheat the oven to 350 degrees F and butter a 9-by-13-inch baking pan.
Beat the cooled brown butter and brown sugar together in a stand mixer fitted with the paddle attachment until creamy. Add the eggs and vanilla and mix, scraping the sides of the bowl. Add the flour, baking powder and salt and mix until combined. Fold in chocolate chips and press the mixture evenly into the prepared pan.
Bake the blondies until a toothpick inserted into the center comes out with only a few crumbs stuck to it, about 35 minutes (I like these blondies gooey, so I go with a little less time). Let cool completely on a wire rack, then cut them and wrap them individually in plastic wrap so the sides don't dry out. Store in the freezer or at room temperature.
This recipe has been updated and may differ from what was originally published or broadcast.