Ingredients
For the lamb
1 leg of lamb, trimmed, weighing around 2-3kg/4lb 8oz-6lb 8oz
2 large onions, quartered
1 leek, thickly sliced
3 sprigs fresh parsley
4 big sprigs fresh thyme
2 bay leaves
salt and freshly ground black pepper
For the sauce
50g/2oz butter
1½ tbsp finely chopped fresh parsley
50g/2oz plain flour
2 free-range egg yolks
90ml/3fl oz double cream
2 tbsp small 'nonpareille' capers
1 lemon, juice only
salt
Method
1. For the lamb, put the lamb into a large heatproof casserole with all the vegetables, herbs, salt and freshly ground black pepper. Cover generously with water, bring up to the boil, skim and then turn the heat down low, so that the water just trembles and shudders at the surface.
2. Cover and leave the lamb to cook gently, topping up with boiling water as necessary, for 2½-3 hours depending on size.
3. For the sauce, about half an hour before the lamb is done, melt the butter in a saucepan over a low heat and add the parsley. Let it stew, not fry, for 10 minutes.
4. Stir in the flour and gradually whisk in 600ml/1 pint of the cooking liquor from the lamb, skimming off any fat before adding to the flour.
5. Bring up to the boil, stirring constantly, then reduce the heat right down and let it simmer for a good 10-20 minutes.
6. In a clean bowl, whisk the egg yolks with the cream, then whisk in a little of the hot sauce.
7. Stir this back into the sauce, and keep stirring without letting it boil until the sauce has thickened slightly.
8. Finally add the capers, lemon juice and salt, then taste and adjust seasoning.
9. To serve, slice the lamb just as if it were a roast leg of lamb, arrange the slices on a hot serving dish and spoon over a little of the sauce. Serve the remaining sauce alongside.
