Preheat oven to 350°F. Line an 8×8 pan with foil, leaving a couple inches overhang. Spray or butter the foil.
Using a hand mixer or stand mixer, beat butter and brown sugar until creamy and combined. Add flour and salt, beat until thoroughly combined. Dump the mixture (it will be crumbly) into the prepared pan and press it evenly into the bottom of the pan. Bake for 15 minutes. Meanwhile, prepare the filling.
In a large bowl, combine melted butter, brown sugar, maple syrup, milk, and egg. Whisk until combined. Add pecans, chocolate chips, and coconut and stir until combined. Pour the filling over the crust and gently spread it around with a rubber spatula so that the solids and liquid are evenly distributed.
Return to the oven and cook for about 23-25 minutes. The mixture should be bubbling slightly around the corners. The edges will be set but the center will still be a little jiggly. It will firm up as it cools. Place pan on a wire rack to cool completely before cutting into squares. Sprinkle lightly with sea salt, if desired, to add a contrast to the sweetness.