Take the puff pastry out of the freezer and thaw it at room temperature until softened.
Peel the sweet potato and cut into 1-cm cubes. Soak it in water for a few minutes, drain and place it into a Lekue steam case. Add 1 and 1/2 tablespoons of water.
Cover the case with the lid and microwave at 600 W for about 3 minutes. Let it sit for 2 minutes to allow it to steam.
Add butter while the sweet potato is still hot. Use a potato masher to mash. Add sugar and milk and mix well.
The moisture content of the sweet potatoes depends on the variety. Adjust the moisture of the sweet potato with milk.
Dust your working surface with cake flour. Roll out the puff pastry with rolling pin until it doubles in size.
Cut the puff pastry into 4 equal sections. Place 1/4 of the filling from Step 4 onto each section. Brush the beaten egg yolk wash onto the bottom half of the dough. (Reserve a small amount of egg yolk.)
Fold the top half of puff pastry over until the edges meet. Using a fork, press to seal the edges.
Pierce some holes in the top with a fork.
Place the prepared pastries onto a parchment-paper-lined cookie sheet. Brush the reserved egg yolk on the tops for glazing and sprinkle some black sesame seeds on top.
Bake the pies in a preheated oven at 200℃ for about 12 minutes or until they puff up and the tops become golden.
Looking for something else? Try this “Pumpkin Pie with Steamed Kabocha Made in a Lekue Silicon Steamer ” (Recipe ID: 1335294)
"Apple Pie with Steamed Apple Made in a Lekue Silicone Steamer": (Recipe ID:1332549)
Try these tuilles made with 1 egg white: (Recipe ID:1334248)
Story Behind this Recipe
Since I could easily cook the sweet potato using a Lekue silicone steamer, I made it into a pie.
Refer to the instructions on puff pastry packaging for the time required to soften the pastry and the baking time. If the pies brown unevenly while cooking, rotate the cookie sheet.