What makes this recipe all the more safe and simple is that the sodium carbonate can be made at home with baking soda (sodium bicarbonate).
Sodium bicarbonate is not actually sodium bicarbonate. That’s an old scientific misnomer that just stuck. Baking soda is actually sodium hydrogen carbonate. And when you get it hot, the hydrogen and oxygen form water and literally boil off, along with some carbon dioxide. … You’ll know exactly when it’s done whenever you stop seeing little gas geysers.
After the dough is boiled for a minute or so in this solution, it is dunked in water as, unlike lye, sodium carbonate doesn’t bake off in the oven. It is then rolled out and into its familiar shape, salted, and put into the oven.
When the pretzels are firm, drop them in the hot water and cook for about 15 seconds — I recommend doing this one at a time. Transfer to the bowl of plain water and rinse clean (the solution tastes bitter). Transfer to a baking sheet and top with coarse salt while it’s still wet (the water will hold the salt in place). Repeat with the other pretzels, and if you want you can score the fat belly of each with a knife to let it puff up more in the oven.
He also recommends brushing the dough with water for a classic shiny look.
Bake until very brown, about 15 minutes. To make the pretzels shinier, you can spray them or paint them with water once or twice during the bake. Easier, though less effective, is to do the same right after they finish baking but are still hot.