Cup of Yum
1. Gather all the ingredients. Preheat oven to 400ºF (200ºC). For a convection oven, reduce the cooking temperature by 25ºF (15ºC). Place 1 sheet frozen puff pastry on a baking sheet lined with parchment paper. Put 1 other sheet frozen puff pastry on a different sheet of parchment paper. Defrost for 10 minutes at room temperature.
2. With a sharp knife, cut the 2 sheets frozen puff pastry in half. Now you have 4 rectangular sheets. For the 2 rectangular half sheets that will go on top, cut 7–8 slits on each sheet, leaving 1 inch (2.5 cm) around the edge.
3. Peel 1 lb Japanese sweet potato (Satsumaimo) and cut it in half lengthwise. Cut into smaller chunks and soak them in water for 10 minutes.
4. In a medium saucepan, put sweet potato and cover it with water. Bring it to a boil and cook until a skewer goes through the potatoes smoothly, about 12–15 minutes. Drain water completely and transfer to a large bowl.
5. Use a potato masher or fork to mash the sweet potato. Add 4 Tbsp sugar and 1 Tbsp unsalted butter and keep mixing.
6. Add 1 large egg yolk and 2 Tbsp heavy (whipping) cream and mix well.
7. Now you put the sweet potato mixture on the bottom pastry sheets, leaving ½ inch (1.3 cm) around the rim. Then cover the sweet potato mixture with the top sheet.
8. With a fork, press down the pastry sheets around the edges to pinch the top and bottom pastry sheets together.
9. Beat 1 large egg (50 g each w/o shell) in a small bowl and brush the top of the pastry so it will turn nice golden brown. Sprinkle 1 tsp toasted black sesame seeds on top (see the image below).
10. Bake for 20–25 minutes, or until golden brown. Let cool for 10 minutes and serve.

To Store

1. You can freeze the baked and cooled pies. Wrap them in aluminum foil and put them in a freezer bag. To serve, reheat the pie at 350ºF (180ºC) for 10–15 minutes, until crisp and flaky.