Remove the seeds, skin, and insides of the kabocha and cut it into bite-size pieces. You can cut the thick skin safely if you cut the kabocha as shown in the picture.
Arrange the kabocha pieces on a microwave-safe plate and cover with plastic wrap, then microwave for about five minutes at 600 watts.
While the kabocha is still hot, add the butter and sugar and mix it all together as the butter melts, creating a paste.
Take the two sheets of puff pastry out of the freezer and let thaw for 5-10 minutes, then cut each one into four parts.
Preheat the oven to 410F/210C.
Take two of the quartered puff pastry, and use a knife to make five slits in the middle.
Pierce the remaining two sheets with a fork in several places.
* Omit, if the puff pastry comes with holes poked in it.
Prepare the other sheet of puff pastry in the same way. * You should have four rectangles with slits in them and four with holes in them for a total of eight.
Leaving 7-8 mm of space on each edge, spoon a portion of the kabocha filling in the middle of each rectangle of puff pastry without the slits.
Place the rectangles of puff pastry with the slits on top of the sheets with the kabocha filling, and using a fork, firmly press the edges of the two sheets together.
Lay parchment paper on a baking sheet, arrange the pies, brush the tops with egg yolk, then bake for 10 minutes in the preheated oven.
After 10 minutes, lower the oven temperature to 360F/180C and bake for 15 more minutes. Then they're done!!
For further reference, here are apple pies made in the same way. Recipe ID: 1335485.
Also, here are some sweet potato pies made in the same way. Recipe ID: 1640427.
Story Behind this Recipe
It'll be Halloween soon, so I thought I'd try making a kabocha version or my basic pie series.
* Please vary the amount of sugar based on the sweetness of the kabocha. * As with my apple pie recipe, because there's not a lot of moisture in the filling, it'll have the texture of a flaky samosa when it's done. If you like, add milk or cream to make the paste less firm.