2 legs of baby lamb -- just under 1 kg each
4 lamb kidneys, cut into small cubes
Fresh thyme and rosemary
1 egg yolk, beaten
1 small glass Madeira
Butter, salt, pepper
Bone the leg of lamb with a thin-bladed knife with a sharp point. Carefully cut along the length of the bone, pulling the meat away from the bone until you reach the ball and socket joint connected to it. Cut through the joint and remove the bone.
In a skillet, heat a little butter and sauté the lamb kidneys. Deglaze the pan with the Madeira; add the thyme and rosemary.
Stuff the bone cavity of the leg of lamb with this mixture.
Reshape the leg of lamb by closing the meat flaps and secure with butcher's twine, with 2 or 3 stitches. Season with salt and pepper.
Rub the leg of lamb with a little butter. Place in a roasting pan in a preheated 250° C oven for about 15 minutes to seal the meat.
Remove from oven and let the meat cool for 10 minutes.
Roll out the puff pastry until 1/8 inch thick; cut into a rectangle with one side wider than the others and wrap the leg of lamb gently in the pastry, like a baby in its blanket.
Brush the top with the egg yolk and return to the oven for 10 minutes until the pastry is golden.