Preheat oven to 350° and butter a 9x13x2 metal baking pan.
Using an electric mixer combine the flour, coconut, powdered sugar and kosher salt into the mixing bowl and mix on low until combined.
Add butter; beat on low until the dough comes together in wet clumps.
With your fingers; press dough onto the bottom and 1/2 inch up the sides of the pan. Bake crust until golden (edges may be darker), for about 20-25 minutes.
MAKE THE FILLING:
Place the sugar and lemongrass into a food processor; pulse until the lemongrass is finely ground, about a minute.
Pour in the lemon juice and process for 30 seconds. Add eggs, process to blend for 10-15 seconds. Add the flour and a pinch of kosher salt; pulse until smooth.
Reduce the heat to 325°.
Pour the lemongrass mixture onto the hot coconut crust and place in the oven for 22-23 minutes or until the filling is firm.
Cool completely in pan on a wire rack. Cut in to twelve squares, dust with powdered sugar and serve!