Shepherd's pie with celeriac

Instructions

1. Cook potato and celeriac in a large saucepan of salted boiling water for 20 minutes or until tender. Drain and return to pan. Heat over low heat for 1 minute to dry out. Add milk and mash well. Season with salt and pepper.
2. Meanwhile, preheat oven to 200°C. Heat oil in a large frying pan over medium heat. Cook onion, carrot, zucchini and garlic, stirring, for 10 minutes or until softened. Add mince and cook over high heat, stirring to break up any lumps, for 5 minutes or until browned.
3. Whisk cornflour, tomato paste, Worcestershire sauce and beef stock in a jug until smooth. Add to lamb mixture and bring to the boil. Reduce heat and simmer for 5 minutes or until thickened slightly. Stir through spinach. Spoon into a 19 cm x 29 cm 2-litre capacity ovenproof dish. Top with tomato slices and spread over mashed potato. Use a fork to create small peaks in the mash. Place dish on a baking tray and bake for 30 minutes or until top is golden.