Boneless loin fillets can also be used for this recipe, however, cooking times will be shorter, dependent on the size. As a guide, cook loin fillets for 10-15 minutes or until the core temperature reaches approx. 68˚C.
Prepare the mint vinegar and the onion oil at least 2 hrs and 30 minutes ahead of cooking the lamb to allow for setting and freezing.
Mint vinegar (used for the mint ketchup and the pickled white onion):
- Bring the white wine vinegar and sugar to the boil in a pan, add the large bunch of fresh mint and let it stand/steep for 5 minutes (like you would make tea), then take the mint out of the pan.
- Pour half of the vinegar mixture into a bowl and set aside, reserving 1-2 teaspoons for the pickled white onion.
- Add the agar agar to the vinegar that’s been left in the pan and bring to the boil, whisking constantly.
- Pour the vinegar/agar agar mixture into a container and place it in the fridge for approximately 2 hours until it sets very hard.
Onion oil (used for the pickled white onion):
- Blend all the ingredients in an electric blender.
- Pass the oil mixture through a muslin cloth over a freezer-proof bowl/jug.
- Place the bowl/jug of oil in the freezer and allow to freeze until the onion oil has separated from the frozen onion water.
- Remove the onion oil from the frozen onion water. (The frozen onion water can now be discarded).
- Reserve a tablespoon of the onion oil for the pickled white onion. You can store the remaining oil in the freezer for future use.
To cook the lamb:
- Prepare the lamb: If your lamb is untrimmed, trim any excess meat and fat away from the bones (watch the recipe video for guidance or ask your butcher to do this for you). Reserve the trimmings. Then using a sharp knife, remove the skin from the lamb, leaving the waxy layer of fat. Score the fat in a criss-cross pattern. Sprinkle the sea salt all over the lamb, rubbing it into the scored fat.
- To make the lamb dressing, place the soy sauce, sake and sugar into a saucepan and mix well. Chop the lamb trimmings and add them to the saucepan, and let it all gently cook on the hob over a very low heat for about 30 minutes.
- Preheat the oven to 120˚C / 100˚C fan / Gas ½.
- Meanwhile, place the lamb in a frying pan over a medium heat. Colour the lamb, fat side down first, applying a little pressure until it becomes golden brown. Then sear both ends of the lamb.
- Place the lamb in an oven tray and cook in the preheated oven for 30-40 minutes (these timings are for medium, where the core temperature of the lamb should be approx. 68˚C). You can adjust the timing to how you like your lamb cooked.
- Once the lamb is ready, take it out of the oven and allow it to rest in a warm place.
- Meanwhile, cook the vegetables and assemble the garnishes.
- Place the asparagus and the Pembrokeshire Earlies in a steamer and cook above salted water. Cook the potatoes for 10-15 minutes or until tender, and the asparagus for 3-5 minutes or until tender.
- While the vegetables are cooking, make the mint ketchup. Turn out the set mint vinegar onto a chopping board and cut into cubes, then add to an electric blender. Add the remaining mint vinegar and blend until smooth and glossy. Pass the mixture through a fine sieve over a bowl and set aside.
- For the pickled white onion garnish, slice the centre of the onion into thin rounds (approximately 2mm thick). Arrange the onion rounds onto a plate and spray or spoon with the 1-2 teaspoons of the reserved mint vinegar. Allow to stand for a couple of minutes, then brush the reserved onion oil onto the onion rounds. Set aside to marinate.
- Once the vegetables are cooked, serve them in separate side dishes and top with butter. Finely chop the fresh mint leaves and sprinkle over the potatoes. Keep warm.
- The lamb should now be well rested. Take it out of the oven tray, and using a sharp knife, cut the meat away from the bones in one piece. Return the boneless lamb to the tray and move it around so it collects all the residual fat from the tray.
- In a medium/hot frying pan, reheat the lamb on all sides – this will refresh it and add some crispiness.
- The lamb is now ready to carve. Trim any extra fat off and carve the meat, on a slight diagonal, into 1cm thick slices. Season with sea salt.
- Arrange the lamb on dinner plates. Top the lamb with the slices of pickled onion, and drizzle the residual marinade over the onion and lamb, followed by one tablespoon of the mint ketchup. Sprinkle with finely chopped fresh mint and finish with the lamb dressing spooned over.
- Serve with the side dishes of steamed and buttered asparagus and Pembrokeshire Earlies.