Easy Basic Sweet Potato Pies

First, make the sweet potato paste.
Chop the sweet potatoes into 1 cm cubes, then in a sauce pan, boil in water filled to the level of the sweet potatoes.
Transfer the sweet potatoes to a bowl, add the light brown sugar, butter, and vanilla essence while hot, then thoroughly mix while mashing.
If the paste is too dry, add milk or heavy cream to adjust to desired consistency.
Preheat the oven to 210C.
Remove the frozen puff pastries from the freezer, thaw for 5 to 10 minutes, then cut each into 4 pieces.
In two of the pieces, make 5 slits in the center of the pastry, as shown.
In the remaining two, prick holes in the pastry with a fork in several places.
For pastries with ventilation holes, skip this step.
Repeat Steps 6 to 7 with the other puff pastry.
You should have a total of 4 pastries with slits and 4 pierced with holes.
In the center of the pastry pierced with holes, place a generous mound of sweet potato paste, leaving a 7 to 8 mm perimeter around the edges (to seal the pastry).
Place the pastry with slits on top, then, press down around the edges using a fork to seal the pastry.
Line a baking tray with parchment paper, arrange the pies on top, brush on the egg yolk wash, then bake in oven for 10 minutes at 210C.
Reduce temperature to 180C, then bake for 15 more minutes, then they're done!
If you have any leftover sweet potato paste, make sweet potato bites..
For Kabocha Squash Pies, see.
For Apple Pies, see.