In a medium bowl, mix together flour and powdered sugar for crust. Cut in butter (I use my hands, but you could also use a fork or a food processor) until the mixture forms a dough.
Pat it into a 9x13 pan and bake for about 10 minutes, until puffed and golden around the edges.
In a medium-sized heavy saucepan, whisk together cornstarch and sugar.
Whisk in the melted butter and half and half. Bring to a boil over medium heat, stirring constantly, until mixture is the consistency of a thick pudding.
Remove from heat and stir in vanilla and coconut.
Pour into pan and spread evenly over crust.
Place pan in the refrigerator and let cool completely.
In a microwave safe bowl, heat chocolate chips and heavy cream, stopping to stir every 20 seconds until smooth.
Stir in light corn syrup and let sit until thickened and cooled.