Wash and boil the Okinawan sweet potato for 30-45 minutes until tender. Peel and mash.

In a medium bowl, combine sugar, flour, and finely chopped macadamia nuts for the crust.

Cut butter into the flour mixture until the texture is sandy.

Press the crust mixture lightly into a 9 x 13 baking pan.

Bake the crust at 325 degrees for 20-25 minutes.

Combine evaporated milk, vanilla, and salt for the sweet potato layer and set aside.

In a large bowl, beat butter and sugar together. Add eggs.

Gradually mix in the mashed sweet potatoes.

Add the evaporated milk mixture.

Pour the sweet potato mixture onto the baked crust layer.

Bake at 350 degrees for 30-35 minutes. Cool completely.

Combine sugar and cornstarch for the haupia layer. Add water.

Pour coconut milk into a medium saucepan. Add sugar mixture. Stir constantly and cook over medium heat until thickened. Allow to cool slightly.

Pour the coconut milk mixture over the sweet potato filling and refrigerate until set.

Cut into bars or diamonds and serve.

Optional: Add a layer of Cool Whip before cutting.