The finished recipe. Lamb Shepherd's Pie with a Sweet Potato Top for FourIngredients 1 to 6. 500 g Lamb mince, lean (Weighed raw.). 700 g Sweet potato (Peeled weight. Three or four medium. Raw, peeled weight.). 200 g Onion. 200 g Carrot. 150 g Frozen peas. 300 g Beef stock (Made up from a cube or a pot.)Ingredients 7 to 11. 2 tbsp (30 g) Tomato purée. 2 tsp, about 10 g Worcestershire sauce. 1 tbsp, about 11 g Olive oil. A few sprigs Fresh thyme. To taste SaltStep 1. Boil the sweet potato in chunks for fifteen minutes until soft. Drain well, mash with salt and pepper and no butter.Step 2. Fry the mince in a dry pan until browned, then tip it into a sieve to drain the fat. Soften the chopped onion and carrot in the oil in the same pan for ten minutes.Step 3. Return the mince with the tomato purée, Worcestershire sauce, thyme and stock. Simmer for fifteen minutes until thick, then stir in the peas.Step 4. Spread the filling in a dish, top with the mash and rough up the surface with a fork. Bake at 200°C for thirty minutes until the top browns at the edges.