In a Dutch oven over medium heat, heat 3 tablespoons of the oil. Add the leeks, fennel and fennel seeds or pollen, season with salt and pepper, and sauté until the vegetables begin to soften, about 5 minutes. Add the wine and cook until reduced by half. Add the stock, cover and cook until the vegetables are tender, about 10 minutes.

Bring a large pot of water to a boil.

Meanwhile, in a heavy frying pan over high heat, heat the remaining 2 tablespoons oil. Add the sausage, breaking it up with a spoon. Cook until well browned, then season with salt and pepper to taste. Pour off most of the fat and add a splash of sherry vinegar.

Generously salt the boiling water, add the pasta and cook until al dente. Save a cup of the pasta water and drain.

Meanwhile, add the sausage to the pot with the vegetables and simmer for 1-2 minutes to meld the flavors. You should have some liquid left in the pot to form a sauce. If not, add a little of the pasta water the pasta was cooked in or more chicken stock. Adjust the seasoning and add a drizzle of olive oil.

Put the pasta in a warmed large, shallow bowl. Add the tarragon, parsley and about 1/2 cup of the cheese. Toss. Add more cheese id desired.