Traditional Lancashire hotpot

Method

1. Preheat the oven to 220°C/ fan200°C/gas 7. Trim the lamb fillet of fat and cut into slices the thickness of a chop. Cut the kidneys in half and snip out the white core. Melt a knob of dripping or 2 tablespoons of vegetable oil in a heavy large pan. Fry the lamb fillet in batches for 3-4 minutes, turning once, until browned. Set aside. Fry the kidneys and cook for 1-2 minutes, turning once, until browned. Set aside.
2. Wipe the pan with kitchen paper, then add the butter. Add the onions and fry for about 10 minutes until softened. Sprinkle in the flour and stir well for 1 minute. Gradually pour in the stock, stirring all the time to avoid lumps. Add the herbs. Stir the lamb and kidneys into the onions. Season well. Transfer to a large 2.5-litre casserole. Slice the peeled potatoes thinly and arrange on top in overlapping rows. Brush with melted butter and season. Cover and bake for 30 minutes.
3. Reduce the oven temperature to 160°C/fan140°C/gas 3 and cook for a further 2 hours. Then increase the oven temperature to 200°C/ fan180°C/gas 6, uncover, and brush the potatoes with more butter. Cook uncovered for 15-20 minutes, or until golden.