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 with an electric mixer on medium-high in a medium bowl 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 macaroon layer: Whisk the egg whites in a large bowl until frothy. Toss the coconut, sugar 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 peanut butter cookie layer (there shouldn't be any peeking through).
Bake until the center doesn't jiggle when shaken and the coconut is golden brown, 55 minutes to 1 hour. Transfer to a rack, and let cool completely.
For the ganache layer: Put the chocolate in a medium heatproof bowl. Combine the cream, butter and salt in a small saucepan, and heat over medium heat until steaming. Pour the hot cream mixture over the chocolate, and let sit for 5 minutes; stir until smooth.
Pour the ganache over the coconut. Cover loosely, and refrigerate until the chocolate is set up, about 30 minutes.
Lift the bar mixture out of the pan, and peel off the foil. Trim to make neat edges, and cut into very small squares, about the size of fudge.