In a large bowl combine the flour, sugar, and chilled chopped butter. Chop the ingredients up using a pastry blender until it starts to have a crumbly texture.
Pour the mixture into a 9x13 pan and evenly spread it out. Flatten the crust using either your hand or a flat object.
Bake for 15-20 minutes.
Sweet Potato Filling:
Boil the potatoes until it is tender enough to pierce a fork through.
Peel and mash the potatoes in a large bowl. Measure out two cups of the mashed potatoes.
Cream the butter and sugar. Then add in the eggs and mix. Gradually mix in the mashed potatoes. Lastly add in the evaporated milk, vanilla extract, and salt. Mix well.
Pour onto the baked crust and bake again for 30-35 minutes.
Haupia Topping:
Combine coconut milk, milk, water, cornstarch, and sugar. Whisk until there are no clumps and sugar particles.
Heat it over medium heat and consistently stir until it thickens and bubbles.
Turn off heat and let it cool for a few minutes.
Pour onto the sweet potato filling and make sure it has spread out evenly. Let it chill in the fridge until the haupia firms up. About and hour or two.
It is optional to top it off with whipped cream. Cut into square pieces and enjoy!