Heat oil in a large heavy-based casserole dish and cook the lamb over high heat for 4-5 minutes until browned. Add garlic and onions. Cook for further 2-3 minutes until softened slightly. Sprinkle the flour over. Toss well to coat.
Add leeks, carrots and bay leaves and pour in stock. Bring to boil, cover and cook for 40 minutes until meat is tender. Remove the lid for final 15 minutes of cooking.
Meanwhile cook the potatoes in a large pan of water for 10 minutes. Drain well. Preheat the oven to Gas Mark 6, 200°C, fan180°C.
Remove the meat and vegetables from heat and add the beans and parsley. Stir well. Layer potatoes on top of meat, lightly brushing with the melted butter as you go, then brush the top with remaining butter. Bake for 1 hour until potatoes are golden.
Freezing and deforsting guidelines
Once the dish has cooled completely, transfer it to an airtight, freezer-safe container, seal and freeze for up to 1-3 months. To serve, defrost thoroughly in the fridge overnight before reheating. Loosely cover with foil and bake until dish is thoroughly heated through. Reheat until piping hot.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.