Macadamia Nut Crust:
Preheat electric oven to 350ºF. Line a 13 x 9x 2-inch baking pan with parchment chopping blade, process the flour and salt until well combined. Add the butter and sugar; pulse until mixture is well combined and crumbly. Add nuts and egg yolk and pulse again until mixture is moistened. Press the mixture lightly into prepared baking pan. Bake for 20 to 25 minutes or until golden brown; cool.
Sweet Potato Filling:
Mash sweet potatoes while still hot. Add sugar, cream cheese, salt, and milk. Mix gently until well combined do not over-mix. Spread the sweet potato filling over macadamia nut crust. Place in the refrigerator while preparing the Haupia Topping.
Reserve 1/4 cup coconut milk; mix with cornstarch; set aside. In a 3 quart saucepan, combine the remaining coconut milk, salt, and sugar over medium heat; bring to boil. Stirring constantly, add the cornstarch mixture and cook until haupia starts to thicken; boil for one minute. Remove from heat; cover saucepan with lid to prevent skin from forming; cool to room temperature. Pour haupia onto sweet potato filling; sprinkle with macadamia nuts or shredded coconut to garnish. Chill for about 2 hours or until haupia is firm. Cut into bars to serve. Makes 12 servings.