Hamburger Potato Buns

1.Cook one large peeled and cubed potato in 1 1/2 cup water with 1/2 tsp salt, cook until soft. Mash the potato with 3 tablespoons potato water, using a fork. Spoon mashed potato mixture into a 1/2 cup measure.
2.Stir mashed potato with buttermilk. Let cool until mixture is warm. Into the potato buttermilk mixture mix honey, yeast and 1 tablespoon flour. Mix well and let sit for 5-8 minutes. Until foamy on the top.
3.Meanwhile, add 2 cups flour and bread flour into a bowl of your stand mixer, stir in 1/4 teaspoon salt and black pepper, set aside.
4.Make a well in the flour, add 2 eggs, butter and pour in all of the yeast mixture. Stir with a wooden spoon until combined, about 30 seconds.
5.Using the mixer with a hook attachment knead yeast dough for 8 minutes, until a soft dough is formed. If the dough appears too wet add up to 1/4 cup flour, adding flour by tablespoons.
6.Dump the dough onto a lightly floured work surface and knead it for 30 seconds to a minute until it becomes to a ball. Return the ball of dough into a lightly oiled bowl, cover and let rise in a warm place for 1 hour.
7.Once the dough has risen take the dough out to a lightly floured surface. Divide evenly into 10 pieces. Shape each piece of a dough into a ball. Transfer onto a baking sheet lined with a parchment or silicone mat. Cover buns with kitchen towel and let rise for 45 minutes.
8.Preheat oven to 375F. In a small bowl add egg and 1 tablespoon water, beat with a fork until well mixed. Brush buns with the egg wash. If using, sprinkle with poppy seeds, sesame seeds, or salt.
9.Bake in the preheated oven, until golden brown about 18-20 minutes. Remove from the oven, and cover freshly baked hot buns with a kitchen towel for 15 minutes. Remove the towel and let cool completely.