Preheat oven to 325 degrees. Line a 9 x 13 baking dish with parchment paper so that it overhangs the sides. ( When completely cooled you can lift the entire out for easier cutting)
Beat the butter, 1/2 cup brown sugar and 1/2 teaspoon salt with an electric mixer until light and fluffy, about 2 minutes. Add 1 cup of the flour and mix until combined. Pour onto the parchment paper. Press the mixture down with a flat cup into a even layer. Bake until golden brown, about 15 minutes. Cool for 20 minutes.
In a medium bowl beat the eggs with the remaining 1 cup brown sugar and vanilla until combined. Add the remaining flour, salt and baking powder. Whisk until incorporated. Stir in the coconut and pecans. Spread mixture evenly over the crust. Bake for 20 - 25 minutes until top is golden brown. Cool completely on a wire rack for at least 2 hours before cutting.
Using the overhung part of the parchment paper (foil can also be used, grease it well) lift from the pan and cut into squares.
Notes
Recipe adapted slightly from America's Test Kitchen.
Recipe by Recipes Food and Cooking at https://recipesfoodandcooking.com/2018/01/03/pecan-coconut-bars/