Okinawan Purple Sweet Potato is different from Purple Yam or Ube in Tagalog. Sweet Potatoes have a smoother outer skin compared to the rough and coarser skin of yams. Sweet potatoes are sweeter, creamier and moist in texture while yams are drier and starchier.
Okinawan purple sweet potatoes are actually native to the Americas (New World) and was only brought to Japan from China sometime between 1492 and 1605. It was brought to Hawaii by the Polenisians (source here), and from there it eventually reached the US mainland.
I bought these purple sweet potatoes after stumbling upon a photo of this online. Since this is only available and sold in Japan, I was challenged to make my own. The problem was there weren’t any recipes available you can follow. The closest I can find is a youtube video which was in Japanese.
This is what I did. Scrub and wash your sweet potato and dry with paper towels. Place these in a baking tray lined with aluminum foil and bake at 400F oven for around 30-40 minutes. You will know it is done when it has a slight give when pinched. Set aside until cool enough to handle.
Get a pre-made pastry crust and let it stand on the counter for a few minutes to soften so that it will be easy to handle. Cut your pie crust into quarters. Lightly grease and flour your boat tart molds. Get one piece and carefully arrange this over your mold and cut of excess with the edge of knife. Prick the bottom of your crust with fork. Repeat the process with the rest of your mold. Bake in a 400F oven until brown, this will only take a few minutes so make sure to watch. Mine took less than 15 minutes. Remove your baked crust from mold and let cool.
Peel off the skin of your sweet potato or you can cut in half to scoop out the flesh. Mash this with a spoon until you get a relatively smooth consistency. Add 1/4 cup butter and stir to combine. Then add 1/4 – 1/2 cup sugar and stir until everything is incorporated. Let this pass through a sieve. Place this in a piping bag with a star tip. Pipe your sweet potato mixture onto your crust. Then bake it again for around ten minutes in a 350F oven until set.
You can serve it warm or at room temperature.
P.S. I intentionally did not add any cream or egg in the mixture since I was not sure how it would affect the color of the purple sweet potato. Maybe next time I will to make it more decadent.
Below is a photo of the unbaked tart and the photo underneath is the baked one. It changes into a deeper color when baked.