Place the duck fat into an ovenproof dish big enough to hold the carrots in a single layer. Place the dish into the oven for 2 minutes to melt the fat. Remove the dish from the oven, place the carrots into the dish and turn to coat in the fat. Season with black pepper and roast in the oven for approximately 40 minutes, turning once during cooking.
Pour the stock into a small saucepan and heat to a very gently simmer.
Heat the butter and olive oil in a large saucepan or skillet over medium heat. Add the leek and garlic and sauté for 3 minutes, or until soft. Add the rice and sauté for 3 minutes, stirring frequently. Pour in the wine and stir until all of the liquid has been absorbed.
Add a ladle (or ¾ cup) of the hot stock to the rice and stir continuously until most of the liquid has been absorbed. Continue adding the stock one ladle at a time, allowing each to be absorbed by the rice, as you continually stir. When all of the stock is used, turn off heat and add the Pecorino, truffle, butter and carrot leaves. Stir to combine.
Garnish with the roasted carrots seasoned with the porcini salt. Finely grate over a little more Pecorino, truffle and drizzle over some virgin olive oil. Serve immediately.
To make the porcini salt – put 15 g dried porcini mushrooms and ¼ cup sea salt into a dry spice grinder. Pulse until very fine. Store in a jar.