In a large measuring cup, combine the water, sugar, and yeast and allow to stand for 10 minutes and the mixture is frothy.

While the yeast is proofing, combine the salt and 4 1/2 cups flour in the bowl of a heavy-duty mixer (or a large bowl, if mixing by hand). Add the melted butter, egg yolk, and the bubbly yeast mixture. Mix until combined. If necessary, add up to an additional 1/2 cup of flour, about a tablespoon at a time, until the dough pulls off the sides of the bowl and barely sticks to your finger when you touch it. Cover the bowl and place it in a warm, draft-free area and allow the dough to rise for an hour or until doubled in bulk.

When the dough has risen, turn it onto a surface lightly sprayed with non-stick cooking spray. Divide into 12 equal pieces or use a scale to measure out 3-ounce pieces of dough. Shape the dough into balls, place on a lined baking sheet (parchment or a silicone liner), cover, and allow to rise for 30 minutes.

While the dough is rising the second time, preheat the oven to 425. Bring 8 cups of water to a boil in a medium saucepan. When the water begins to boil, add the baking soda and bring back to a full boil. Working with one roll at a time, carefully place each roll, seam-side down into the baking soda bath. Boil for 30 seconds then flip and boil for another 30 seconds. Use a slotted spoon to remove the boiled roll from the water and place, seam-side down, on the baking sheet. Repeat with remaining dough balls.

Whisk together the reserved egg white and 2 tablespoons of water. Brush the egg white over the boiled dough balls and then sprinkle with kosher salt. Bake for 12-18 minutes or until the tops are golden brown. Remove from oven and cool on baking sheets.