How to Make It
In a saucepan, heat the milk just until simmering. Remove from the heat and add the pretzels. Cover and let stand until softened, about 30 minutes. Strain the pretzels, pressing to remove as much milk as possible. Transfer the pretzels to a bowl.
Meanwhile, in a small skillet, melt 1 tablespoon of the butter. Add the onion and cook over moderate heat until softened, about 7 minutes. Scrape the onion into the bowl with the pretzels and add the parsley. Season with salt and pepper. Let cool slightly, then stir in the egg.
Set a 14-inch-long sheet of plastic wrap on a work surface. Spoon the dumpling mixture on top and wrap the plastic around the mixture, shaping it into a 6-by-2-inch log. Tie the ends. Wrap the dumpling again in the plastic and tie the ends again.
Bring a saucepan of water to a simmer. Add the wrapped dough and weight it down with a heavy lid. Cover and simmer over low heat until the dumpling is firm, about 25 minutes. Carefully transfer the dumpling to a work surface and let cool. Unwrap it and cut into six 1-inch-thick slices.
Melt the remaining 2 tablespoons of butter in a large nonstick skillet. Add the pretzel dumplings and cook over high heat, turning once, until browned and crisp, about 5 minutes. Serve right away.