Make the noodle base and sauce first - put the sesame paste or tahini mixture, the chilli oil and vinegar into a small wok or pan, add the stock and bring to the boil. Reduce the heat to low while you cook the noodles and make the meat topping and garnish.
Cook the noodles according to the packet instructions then drain and toss them through with some toasted sesame oil. Put to one side.
Now make the meat topping, heat a wok over a high heat and add the groundnut oil. Add the garlic, ginger and chilli and stir-fry for a few seconds, then add the minced beef. As the beef starts to turn brown, add the rice wine or sherry and cook for a few seconds. Stir in the cornichons or gherkins and cook until fragrant, then season with the soy sauce and keep on a very low heat.
For the garnish, put the Sichuan peppercorns into a small pan and dry roast until fragrant, then remove from the heat and crush in a pestle and mortar, or place in a plastic bag and bash with a rolling pin
To serve, divide the noodles between four bowls, then ladle on the sauce and top with the meat. Garnish with the Sichuan peppercorns, spring onion and coriander. Drizzle chilli oil over the dish, add a drizzle of sesame oil, to taste, around the edge of the sauce and serve immediately, with extra chilli oil if you like.