To start the pomme puree, cover a baking tray with rock salt, place the potatoes on the bed of salt and bake for 1 hour. Remove from the oven and keep warm.
Trim all backstraps to 180g. Try to keep the fillets the same width and length if possible. Season the offcuts with salt and pepper for the jus. To make the lamb jus, heat the olive oil in a large saucepan over high heat, add the reserved lamb trimmings and cook for 5 minutes until caramelised. Stir in the shallot, carrot and celery and season with salt and pepper. Sauté for 3–5 minutes until the vegetables begin to brown. Stir in the garlic and rosemary and sauté for 2 minutes. Deglaze the pan with the wine and flambé. To flambé, tip the pan carefully away from you but towards an open flame, allow the vapours to ignite and keep the pan at arm’s length. Allow the alcohol to burn off naturally before you continue cooking.
Pour in the stock, one ladle at a time, allowing the liquid to reduce by half each time. Once all the stock has been incorporated, strain the jus into a clean saucepan and reduce the jus to your desired consistency. Season with salt and pepper to taste. Keep warm.
Heat a little olive oil in an ovenproof frying pan on high heat. Place the onion halves, cut side down, in the pan and cook until completely blackened. Transfer to the oven for 25 minutes. Remove and allow to cool before separating the onion petals.
In a large ovenproof frying pan, sauté the carrots in olive oil on high heat for 2 minutes. Season with salt and pepper, drizzle with the honey, add a squeeze of orange juice and cook for another 2 minutes. Transfer to the oven to roast for 15 minutes.
Season the lamb backstraps with salt on both sides. Heat a frying pan or chargrill pan over high heat and cook the backstraps for 2 minutes on one side, then turn and cook for 90 seconds on the other side. Remove from the heat and allow to rest for 5 minutes.
To finish the pomme puree, scoop the insides from the potatoes into a sieve and then push the potato through the sieve into a saucepan. Add the butter and cream and whisk over low heat until smooth then season with salt and pepper.
Place a lamb backstrap on a plate, add two spoonfuls of the pomme puree, a small stackof carrots and three of the onion petals. Fill the onion petals with the jus.