Drizzle beef with sunflower oil in a bowl and toss to coat. Toast Szechuan peppercorns in a small frying pan until fragrant, do not burn. Tip into a mortar and pestle and grind to a fine powder.
Place a large cast iron casserole dish or wok over medium high heat. Brown beef in 2-3 batches, add ground peppercorns, onions, carrots, parsnip, garlic, chilli, soy, sesame paste and stock and bring to the boil. Cover and simmer for 1 hour 15 minutes or until beef is tender.
Mix a few tablespoons of the cooking liquid with the cornflour to a smooth paste and stir into mixture. Cook for 5-10 minutes until mixture thickens. Add spring onions.
Meanwhile steam sweet potato and mash with ginger. Preheat oven to 200oC. Divide pie filling between 4 x 1 cup-capacity ramekins and top with sweet potato topping.
Bake pies for 15 minutes or until golden and serve with steamed greens.
Szechuan peppercorns are available from Asian grocers or the Asian section in supermarkets. If you don't have a mortar and pestle to crush the peppercorns you can place them in a zip lock bag and whack them with a rolling pin.
If you don't have toasted sesame paste or tahini substitute 1 teaspoon sesame oil mixed with 1 teaspoon peanut butter.
Make one large pie by using a 4-cup capacity baking dish or 8-9 inch pie plate.
Save time and use lean beef mince instead of chuck. Reduce the cooking time to 30 minutes and only use half the stock.