- 1 tblsp rapeseed oil
- Knob of butter
- 3 onions, thinly sliced
- 1.5kg (3lb) potatoes, peeled and thinly sliced
- 4 fresh thyme sprigs, leaves stripped
- 400ml (14fl oz) chicken stock
- 1.75kg (4lb) leg of lamb
- 3 garlic cloves, sliced
- 2 fresh rosemary sprigs
- Sea salt and freshly ground black pepper
- Wilted spinach (see link below), to serve
- Preheat the oven to 200°C (400°F/gas mark 6).
- To make the Boulangère Potatoes, heat the oil in a frying pan with the butter and sauté the onions for 3-4 minutes over a medium heat, until softened but not coloured. Season to taste.
- Layer the potatoes, onions and thyme leaves in a large roasting tin large enough to fit the leg of lamb. Season each layer as you go and finish with an attractive overlapping layer of the potatoes. Pour over the stock and set to one side.
- Using a sharp knife, make small incisions all over the lamb and press a garlic slice and a tiny sprig of the rosemary into each one. Weigh the joint and allow 20 minutes per 450g (1lb) plus 20 minutes (add a further 20 minutes for well done), then place the lamb carefully on top of the potatoes in the roasting tin. Roast for 20 minutes, then reduce the oven temperature to 180°C (350°F/gas mark 4) and roast for 1 hour 20 minutes for a leg of lamb this size (1.75kg (4lb)).
- Transfer the leg of lamb to a carving platter and cover loosely with foil, then leave to rest for 15 minutes, keeping the Boulangère Potatoes warm.
- To serve, carve the lamb into slices and arrange on warmed serving plates with the Boulangère Potatoes and wilted spinach.