Combine the warm water, sugar, and active dry yeast in a large bowl. Let the mixture stand for 5 to 10 minutes, until foamy, which indicates that the yeast is active.

Add the salt and slightly cooled melted butter. Mix in about 4 cups of flour, then add the remaining flour gradually until a soft, slightly tacky dough forms.

Knead with a dough hook for 5 to 7 minutes, or by hand for 8 to 10 minutes, until the dough is smooth and elastic. Place it in a lightly greased bowl, cover, and let it rise in a warm place for 60 to 90 minutes, or until doubled.

Deflate the risen dough and divide it into 8 equal pieces for large rolls, or 10 to 12 pieces for smaller rolls. Shape each piece into a tight round by pulling the dough underneath and pinching the seam closed.

Cover the shaped rolls and let them rest for 20 to 30 minutes. During this rest, preheat the oven to 425°F (220°C) and line baking sheets with parchment.

Bring 8 to 10 cups of water to a simmer or gentle boil in a large pot. Carefully add the baking soda because the mixture will foam at first.

Lower the rolls into the baking-soda bath, working with 2 to 4 at a time. Simmer for about 30 seconds per side, or 30 to 60 seconds total, then remove them with a slotted spoon.

Place the bathed rolls on the prepared baking sheets. Brush each one with the egg wash, score the tops if desired, and sprinkle with coarse pretzel salt or flaky salt.

Bake at 425°F (220°C) for 14 to 18 minutes, rotating the pan once if needed, until the rolls are deeply browned. Cool for at least 10 minutes before serving, and brush with melted butter immediately after baking if you want an especially soft crust.