For the stock, place a large, deep saucepan onto a high heat. Fry the deer trimmings for about five minutes or until browned on all sides, then add the carrot and shallots and cook for four minutes, stirring from time to time, until the vegetables are starting to caramelise. Add the thyme and bay leaves along with the cold water and game stock. Bring to a boil and gently simmer, uncovered, for 40 minutes. Strain the liquid through a fine sieve into a clean pan and cook until reduced for a further 20 minutes. Strain through a muslin-lined fine sieve and keep warm.
Meanwhile, place the lentils and bay leaf into a saucepan and pour in enough cold water to cover the lentils. Bring to a boil, then simmer for 20-25 minutes or until the lentils are tender, adding more water during cooking if needed. Drain well then remove the bay leaf, spread the lentils evenly onto a baking tray to cool and set aside.
Place a dry pan on high heat. Add the pancetta, half the diced carrots and half the diced shallots. Cook for 2-3 minutes, or until the pancetta is crisp and the vegetables are slightly tender, then stir in half the lentils and cook for 40 seconds. Transfer the mixture to a large mixing bowl, drizzle with extra virgin olive oil and toss through the thyme. Season with salt and freshly ground black pepper and set aside until needed.
For the fricassée, boil the diced potato in a pan of salted water until tender. Drain well and spread out onto a tray to stop them from cooking further. Melt the butter in large frying pan until it begins to foam, then add the fresh porcini mushrooms and the garlic and cook gently for 3-4 minutes, or until the mushrooms are golden-brown and tender. Stir in the thyme and cook for one minute until fragrant. Peel and finely chop the cooked garlic and stir into the mushroom mixture. Gently combine the potato, mushroom mixture and diced dried porcini. Season to taste with salt and freshly ground black pepper and cover to keep warm.
For the deer, heat the butter and thyme springs in a frying pan until butter begins to foam. Increase the heat and sear the deer fillets for about two minutes on each side. Transfer the fillets to a plate, cover and set aside to rest in a warm place. Reserve the pan for later use. Add the juices released from the rested meat to the reduced stock.
To make the jus, place the pan used to seal the deer over a high heat. Add the red wine, flambé then reduce the volume of liquid by half and add the deer stock. Stir in the chocolate, whisk in the chilled butter and reduce until syrupy and glossy.
To make the velouté, gently cook the celery in a saucepan with a little olive oil along with the remaining carrot and shallot for 3-4 minutes, or until the vegetables are tender. Stir through the remaining lentils and cook for a further 2-3 minutes, or until the lentils are very soft. Season with salt and freshly ground black pepper, then pulse in a food processor until smooth. Push the mixture through a fine sieve into a clean saucepan. Just before serving, stir in the cream, bring to a boil and simmer uncovered until slightly thickened.
Five minutes before serving, place the slices of lardo in a dry frying pan and gently heat to render out the fat. Turn the heat up, add the deer fillets and cook for two minutes on each side, basting with the fat as they cook. Remove from the pan and leave to rest in a warm place for a couple of minutes before serving.
Arrange the fricassée in the centre of the plates and top with thick slices of the deer fillet. Scatter the warm lentil salad around the plates and pour over the lentil velouté. Finish with a drizzle of the jus and garnish with fresh thyme leaves.