Step 1

In a large bowl, using an electric mixer fitted with a hook attachment, add the flour, potato flour, sugar, salt, yeast, milk, and eggs, and knead on low speed until it comes together about 3-4 minutes. Scrape down the sides of the bowl halfway through. Let rest for 20-30 minutes.

Step 2

Knead on low speed and gradually add the butter until it is completely incorporated. Once all of the butter is incorporated, increase the speed to high and knead for about 4-6 minutes until the dough is smooth, releases from the sides of the bowl, and passes the windowpane test. It's a very soft, smooth, and satiny dough that is slightly tacky to the touch. If you find that you need to knead a few minutes longer to pass the windowpane test, give the dough a short break for a few minutes to avoid overheating the dough. Otherwise, the yeast could cripple.

Step 3

Lightly spray a straight-sided container with oil and transfer the dough to the container; lightly oil the top of the dough as well. Cover and let rest at room temperature for 10-20 minutes until it has grown by about 10-20%. Then put it in the refrigerator and let rest overnight, about 8-12 hours. It will at least double in this time.

Step 4

Remove the dough from the refrigerator and let it rest at room temperature for about 30 minutes.

Step 5

In the meantime, line a 9x13-inch (23-33cm) baking pan with parchment paper and lightly spray with oil. Set aside.

Step 6

Remove the dough from the container with a dough scraper and place it on a very lightly oiled work surface. Roughly shape the dough into a square and divide it into 15 equal pieces.

Step 7

Apply a little oil to your fingers, take one piece of dough, roll it into a ball, and deflate it while you roll it up. Then stretch up the dough on the side farthest away from you and fold over the center. Then rotate the dough by about 45°, stretch the dough farthest away from you and fold it over the previous fold and over the center. Repeat this 6-8 times. You will notice that the dough builds up tension and becomes firmer with every fold. The goal is to have a round ball with all the seams on one side.

Step 8

Then place the dough ball seam side down, gently cup it with one hand, and form a C-shape with your hand. Move the dough with your hand in a circular motion and gently press it against the work surface to build tension, stretch the surface of the dough, and close the seams at the bottom. If the dough is a bit sticky, oil your hands very lightly. Avoid using flour on the work surface to allow the dough to anchor to the surface as it moves. Do this gently without tearing the surface of the dough, and don't overwork the dough. Repeat with the remaining pieces of dough.

Step 9

Arrange the dough balls in the prepared baking pan in 3x5 rows with the same distance between the individual dough balls. Let sit at room temperature for 45-90 minutes until they have doubled.

Step 10

In the meantime, preheat the oven to 400°F (204°C) for 15-20 minutes.

Step 11

Brush the dough balls with egg wash and bake for 15-20 minutes until golden brown.

Step 12

Remove from the oven, brush with melted butter, and cover with a clean and dry kitchen towel for 20 minutes. Then uncover and transfer to a cooling rack to cool completely. Store in an airtight container at room temperature for up to 4 days.