In a large pan, add a drizzle of olive oil and heat over medium-high heat. Add the sliced leeks and stir. Cook for around 10 minutes until softened and sweating down.
Meanwhile, use a knife to score along the side of each sausage and remove from the casing. Once the leeks are soft, remove from the pan.
Add the sausages to the pan and use a spatula to break them apart into small pieces. Add the fennel seeds. Fry for 10 minutes roughly, or until browned and crispy on at least one side. Add the garlic and stir. If using, add the wine to the pan and stir around. Really scrape up any burnt bits on the bottom of the pan. Then add the leeks back to the pan.
Add the stock and mascarpone to the pan, snap in the lasagne sheets into large pieces. Mix together, season well and bubble gently (lid off) for around 15 minutes, or until the pasta is soft and most of the liquid has been absorbed. It may take closer to 20 minutes.
Stir through some fresh basil, if you have it, and serve with dollops of mascarpone on top and lots of black pepper.
