How to Make It
Preheat oven to 450°F. Bring water and baking soda to a boil in a large saucepan over high. Divide dough into 6 equal pieces, and roll each into a 1-inch-thick rope (about 9 inches long); cut into 1½-inch pieces.
Boil dough pieces, in batches, until slightly puffy, about 20 seconds. Using a slotted spoon, transfer pieces to a lightly greased baking sheet; brush with egg, and sprinkle with salt. Bake in preheated oven until deep golden brown, 10 to 12 minutes. Serve with mustard.