For the pea purée:
- Bring to a boil a pot of salted water with 100g of butter. Add the peas and cook for up to 5 minutes, until tender.
- Remove from heat and drain the liquid, but keep it to the side.
- With the help of a stick blender or blender, start blending the peas and add gradually the cooking liquid until you obtain a thick but smooth purée. Check seasoning. Place the puree into a bowl on top of ice cold water. Place in the fridge.
For the lamb:
- Cook the jersey royal, mint, salt and water. Bring to a boil and cook until firm and soft.
- Blanch the leeks in boiling salted water. Remove, and cool down under cold running water.
- Add oil into a hot pan. Place the lamb skin side down into the pan and brown until it is coloured on all sides.
- Place onto a roasting tray, place into an oven preheated to 180 degrees Celsius, and cook for 15 minutes. Then, rest for 6 minutes.
- Turn the grill on to max heat, and while the lamb rests, grill the leeks cut side up until blackened.
- Arrange on a large plate.