Peel the potato and cut into 1-inch cubes. Place into a small pot and cover with cold water by a couple of inches.

Bring to a boil, then reduce heat and simmer until tender, about 10 minutes.

Drain very well and mash until perfectly smooth. Let cool to no more than 110°F before proceeding.

Into the bowl of a stand mixer fitted with the dough hook (or a large mixing bowl, if you plan to knead by hand), place the bread flour, powdered milk, sugar, salt, and yeast. Whisk to combine well.

Add the water, honey, butter, mashed potato, and beaten egg.

Mix on low speed (number 2 on a KitchenAid mixer) until combined, and then let the machine run to knead the dough until it is fairly smooth and elastic, two to four minutes more. Dough will still be soft and sticky but should hold together.

Pour the safflower oil into a clean bowl and swirl to coat the bottom. Scrape dough out of mixer into bowl and turn to coat with oil.

Cover with plastic wrap and let rise until doubled in size, an hour or two depending on the the temperature of your kitchen.

Turn the dough out onto a lightly floured surface and use a bench knife to divide into 10 equal pieces. I like to weigh them for evenness — they'll be about (102 grams) each, depending on the size of your potato.

To shape each piece, fold the corners in to create a rough round shape. Flip the round over so that the seam is on the bottom. Then use a circular motion to guide the bun along your work surface between your thumb and the heel of your hand. This increases surface tension and eliminates the seam. You can see this process in action in the video that accompanies this post.

Arrange buns three inches apart on a silpat- or parchment-lined half sheet pan. Gently flatten each one with the palm of your hand.

Cover again and let rise until substantially puffed, about an hour.

Preheat oven to 350°F with a rack in the center.

To make the egg wash, use a fork to whisk together the egg and milk in a small bowl.

Brush the buns with egg wash. If you like, you can sprinkle them with sesame seeds, poppy seeds, or everything but the bagel seasoning.

Bake for about 24 minutes, until golden brown on top and cooked through.

Remove from oven and let cool on pan on a cooling rack for a few minutes, then transfer buns directly to rack and let cool completely before proceeding.

To serve, use a serrated knife to slice each bun in half horizontally.

If you like, heat a cast iron skillet over medium-high, lightly spread the insides of each bun with softened butter, and toast on the skillet for a few minutes, until crisped and golden brown.