1Bring a large saucepan of water to a boil. Stir in the egg noodles and cook until just tender, about 8 minutes. Drain, transfer to a bowl, drizzle the sesame oil over them, toss to coat, and reserve.
2For the meatballs: Mix together the beef, pork, ginger, fish sauce, vinegar, chili flakes, peppercorns, salt, some black pepper, the scallions, garlic and egg yolk in a large bowl until well combined. Roll the mixture into 12 meatballs using your hands, wetting them if necessary.
3Heat the oil in a wok over high heat and fry the meatballs, working in batches and turning with a slotted spoon until golden and cooked through, 4 to 5 minutes. Transfer to a paper-towel-lined plate to drain. Drain the wok and wipe it clean with a paper towel.
4For the sauce: Heat the peanut oil in the wok over high heat. Add the shrimp paste and stir-fry until toasted, and then stir in the lemongrass and coconut milk and boil until reduced by half, about 5 minutes. Add the fish sauce, Sriracha and cooked meatballs and briefly simmer to reheat them in the sauce. Transfer the meatballs to a plate. Toss the noodles in the sauce until well coated and hot.
5Transfer the noodles to a platter, top with the warm meatballs, and garnish with chopped cilantro sprinkled over the top. Serve immediately.