Butter a 9-inch pie plate. In a bowl, combine flour and salt. Cut in the shortening and margarine till mixture resembles coarse meal.
Gradually add ice water to the mixture while mixing with a wooden spoon until dough is formed.
Pour the dough onto a lightly-floured sheet of clingwrap and form into a disc. Lightly flour the top of the dough and place another sheet of clingwrap on top. Roll dough out till 1/8-inch thick.
Remove the top piece of clingwrap, lay dough across pie plate and remove the bottom piece of clingwrap. Press dough down lightly. Lightly prick the dough with a fork. Bake at 200˚C for 10 - 12 minutes, then remove and allow to cool.
To make coconut custard:
Pour all ingredients except margarine into a saucepan over medium-low heat, and bring to a boil, stirring, for 1 minute. Remove from heat and add margarine.
Spread custard into pie crust. Cover lightly with plastic wrap and chill until set, about 30-45 minutes.
Whisk vanilla into whipped cream until just combined.
Spread cream on top of coconut custard. Chill until ready to serve.