Recipe: Modified from "Okinawan Sweet Potato Pie with Haupia Topping" reprinted in "Best of the Best from Hawaii Cookbook: Selected Recipes from Hawaii's Favorite Cookbooks" edited by Gwen McKee and Barbara Moseley. The recipe is originally from "Hawai'i's Best Local Desserts".
Status: Made once.
This pie has a vibrant purple layer (made from Okinawan sweet potatoes which are naturally purple), a rich coconut milk layer, and a delicate shortbread pie crust. Since the Okinawan sweet potatoes taste similar to chestnuts or taro, this pie is reminiscent in flavor (but not texture) to a Chinese-style chestnut filled cake (a moist spongey cake layered with chestnut purée and topped with a whipped cream icing). I made this for Thanksgiving, as an unusual Asian-inspired take on a Thanksgiving sweet potato pie, but this pie can be made any time of the year.
Okinawan sweet potatoes have tan or brown skin and a dark purple flesh that becomes even more vibrant when cooked. They have a dry dense texture, taste sweet, and are similar in flavor to chestnuts or taro. This pie must be made with Okinawan sweet potatoes; other types of yam or sweet potatoes cannot be substituted. They are most likely to be found in Hawaiian or Japanese grocery stores.
Press-In Shortbread Crust:
- 2 Tbsp sugar
- 1-1/2 cups flour
- 1-1/2 sticks cold butter (12 Tbsp) (3/4 cup)
- (optional) 1/2 cups chopped toasted Macadamia nuts
- 1 stick room temperature butter (8 Tbsp) (1/2 cup)
- 1 cup sugar
- 2 eggs, beaten
- 2 generous cups Okinawan sweet potato
- 1/2 cup evaporated milk
- 1 tsp vanilla
- 1/4 tsp salt
- 2/5 cup sugar (about 6.5 Tbsp)
- 2/5 cup cornstarch (about 6.5 Tbsp)
- 1-1/8 cup water (1 cup + 2 Tbsp)
- 1 can (19 oz) coconut milk (e.g. May Ploy brand)
- 1/4 tsp salt
Press-In Shortbread Crust:
Preheat the oven to 325 F. Butter or lightly oil a baking pan you would like to use (you can use a pie pan if you would like to make slices of the pie, or you can use a rectangular or square shaped baking pan if you would like to make bars or squares.). Combine sugar and flour. Cut or use your fingers to rub the butter into the flour mixture until sandy. You can place the mixture in the refrigerator or freezer for a few minutes to cool, if the butter becomes too soft or starts to melt and then continue your work when the mixture is colder.
Press the crust mixture lightly into the bottom baking pan as evenly as possible. If you are using a pie pan, then press the crust mixer lightly onto the sides of the pan and use a table knife to cut the top of the crust to an even length. If you are using a rectangular or square shaped baking pan, there is no need to press the crust mixture onto the sides (The Okinawan sweet potato filling which touches the sides of the baking pan may turn brown after baking; if so you can trim off a thin slice of the brown edges before cutting the pie into squares or bars). Freeze the crust for at least 30 minutes to harden the butter.
Bake at 325 F for 20 - 25 minutes, or until the crust is pale but very lightly browned. Let cool.
Okinawan Sweet Potato Filling:
Preheat the oven to 350 F.
You can cook the Okinawan sweet potatoes by baking, boiling, or steaming them. I suggest steaming them whole, since this best preserves their color and moisture.
When the Okinawan sweet potatoes are cool enough to handle, peel them and then mash them. I suggest using a potato ricer to get the finest consistency so that the pie has a smooth texture.
Beat the butter and sugar. Mix in the eggs. Gradually mix in 2 cups of mashed Okinawan sweet potatoes. Add the evaporated milk, vanilla, and salt. Slowly increase the mixing level to medium-high and whip the mixture as you would to make whipped potatoes (e.g. to level 8 out of 10) in order to incorporate air into the filling.
Pour the filling into the crust; stop when it fills the crust halfway. If you have extra filling, you can bake it in another pan to make a crust-less pie or you can make an additional crust to bake it in (the pie tastes best with the shortbread crust).
Cover the edges of the pie with aluminum foil so that the edges won't become overly browned. Bake at 350 F for 30 to 35 minutes, or until a toothpick comes out clean, but preferably still has some moisture or a few crumbs stuck to it (this indicates that the filling is cooked through but still moist). Cool.
Haupia Topping (Coconut Pudding):
Mix sugar, salt, and cornstarch in a medium pot. Stir in water and blend well. Add the coconut milk. Cook over medium-low heat, stirring constantly, until the mixture thickens, but doesn't boil. It will become very thick, similar to a frosting.
Cool slightly, and then pour the haupia over the pie filling, until the haupia covers the pie and nearly fills the crust (a small portion of the sides of the crust should peek out above the haupia). Use a spatula to smooth the top of the haupia topping.
If you have extra haupia or if you baked extra filling in another pan, then you can spread the extra haupia in another pan and serve it as a separate dessert after it has solidified or you can spread it over the extra baked filling.
Refrigerate; the haupia will become solid, similar in texture to Jello and other gelatin desserts.