Bring a large pot of water to a boil and salt it. In a smaller pot, bring 6 cups of water to a boil; once boiling, reduce heat so water bubbles gently. To the smaller pot add soy sauce, ketchup, vinegar, sesame oil, if using, and sriracha or chile, along with a pinch of salt. Stir and let simmer. Add egg noodles to large pot. Cook's Note: Fresh noodles will be ready in just a couple of minutes; dried will take longer. When tender, but not mushy, drain. Taste broth and add more soy, salt, vinegar, or heat as you like. Divide the noodles into bowls and pour hot broth over all.
Recipe courtesy of Mark Bittman