We combined a peanut butter cookie, a brownie and a macaroon and made something totally wonderful-and definitely worth the effort. The bars are almost like fudge, so a little goes a long way. Bonus: This triple-threat dessert smells amazing as it bakes!
Position an oven rack in the bottom position of the oven, and preheat to 350 degrees F. Line a 9-inch square baking dish with foil, leaving an overhang on all sides. Coat the foil with cooking spray.
For the peanut butter cookie layer: Beat the peanut butter, sugar and salt in a medium bowl with an electric mixer on medium-high until smooth. Beat the eggs in one at a time and then the vanilla. Adjust the speed to medium-low, add the flour and beat until incorporated. Press the batter into an even layer in the bottom of the prepared baking dish; set aside.
For the brownie layer: Combine the flour, cocoa powder and salt in a medium bowl; set aside. Melt the butter and chopped chocolate in a medium saucepan over medium heat, stirring, until smooth, about 4 minutes. Remove from the heat; let cool slightly, then stir in the sugar. Mix in the eggs until combined. Stir in the flour mixture and then the chocolate chips until just combined. Pour the brownie batter over the peanut butter layer.
For the macaroon layer: Whisk the egg whites in a large bowl until frothy. Toss the coconut, sugar, vanilla and salt together with your hands in another large bowl; add the egg whites, and stir until the coconut mixture is coated. Scatter the coconut mixture in an even layer on top of the brownie layer (there shouldn't be any brownie peeking through).
Bake until the center doesn't jiggle when the pan is shaken and the coconut is golden brown, 1 hour 10 minutes to 1 hour 20 minutes. (A knife inserted in the middle will still come out wet, because the brownie layer is super fudgy. The jiggle cue is the key to determining doneness.)
Transfer the pan to a rack, and let the bar mixture cool completely, preferably overnight. Lift it out of the pan, and peel off the foil. Trim the bar mixture to make neat edges, and cut into very small squares, about the size of fudge.