preheat oven to 350*.spread coconut in an even layer on a rimmed baking sheet -- bake, stirring, once or twice.until golden.
about 8-10 minutes.let cool completely.
process cookies and 1/2 cup coconut in a food processor till finely ground -- and mixture clumps together.about 2 minutes.
transfer mixture to a 9x13" pan -- press even layer on bottom.bake 12-15 minutes.let cool on wire rack.
whisk together granulated sugar, cornstarch, salt in large pan -- whisk in milk and egg yolks.cook over medium heat whisking constantly till it comes to a boil.about 5-6 minutes.continue to cook, whisking about 3 minutes or thick.
remove from heat and add butter.whisk till combined and thoroughly melted.