How to Make It
Preheat oven to 350°F. Grease a metal 9- x 13-inch baking pan with cooking spray. Line the bottom with a fitted rectangle of parchment paper. Set aside.
In a small saucepan, heat butter over medium-high heat, swirling often and scraping the bottom of the pan with a heatproof spatula, until butter foams and then browns, about 4 minutes. Set aside to cool for 1 minute.
In a mixing bowl, stir together browned butter, sugar, and milk until combined. Add all-purpose flour, 1/4 tsp. kosher salt, and chopped pecans. Stir with a large spoon until dough forms. Spread and press evenly into the bottom of the prepared baking pan. Bake until lightly browned on the surface, about 18 minutes.
While crust is baking, whisk together brown sugar, granulated sugar, remaining 3/4 tsp. kosher salt, all-purpose flour, and baking powder until well combined. Add eggs and vanilla, and whisk until there are no more dry pockets. Stir in sweetened coconut.
When crust has finished baking, pour the liquid mixture on top of the crust. Sprinkle the surface evenly with the unsweetened coconut chips. Bake until the coconut has toasted and the filling has set, about 20 minutes. Allow to cool to room temperature before cutting.