Combine the water and yeast in bowl of electric stand mixer fitted with dough hook, and let rest 5 minutes, until foamy.
Add the sugar, flour, salt, and butter, and mix with the dough hook until thoroughly combined. The dough will come together and start to feel silky rather than sticky.
Cover the bowl with a towel and let the dough rise in a warm place for 1 hour, or until doubled in bulk. (If you have a bread proof option on your oven, I recommend this for consistent temperature.)
While the dough is rising, line two sheet pans with parchment paper or Silpats, and set them on the counter. If you have a scale, get that ready as well.
Turn the dough out onto a lightly floured surface, and knead it gently to deflate it (I learned at King Arthur that you should be nice to the dough and not punch it down).
Cut the dough into 18 pieces, roughly 2 ounces each. (If you have a scale, you can weigh the dough and portion it out.)
To shape, place a piece of dough on the counter and form a cage around it with your fingertips. Rotate your hand in small circles, rolling the dough around against the counter. This should create a nice, round smooth ball of dough with a "belly button" on the bottom.
Place as many rolls as you'd like to make that day on one sheet pan, spaced evenly, belly-button down, at least 1 inch apart. Toss a little flour on the other sheet pan, place the rolls you'd like to save for another time on that pan, and toss it in the freezer.
Cover the rolls you left out with a towel, and let them rise in a warm place for 30 minutes, or until doubled.
Preheat oven to 425°F.
In a large pot, bring 2 quarts of water to a low boil (or 1 quart if you're not poaching the full batch of rolls).
Add the baking soda, and lower the heat to a simmer.
Carefully slip the rolls into the poaching liquid, belly button-side down. Poach for 30 seconds, and then carefully turn the rolls over in the liquid. Poach other side for 30 seconds, and then using a spider or skimmer, transfer the rolls back to the sheet pan, belly button-side down. Repeat with the remaining rolls.
Using a pastry brush, glaze each roll completely with the lightly beaten egg, making sure to coat all sides completely.
Top each roll with a sprinkle of pretzel salt or kosher salt.
With a sharp, straight-edged knife, cut a slash in the top of each roll.
Bake the rolls for 12 to 18 minutes, rotating the pan halfway through baking for even browning.
Let cool slightly, and dig in! I ate mine with butter, but mustard and cheese are always good alternatives!