Add a good splash of olive oil to a large pan on medium-high heat. Add the onion and fry for 2 to 3 minutes until soft and starting to brown. Add the garlic and fry another 1 minute. Add the celery and carrots and fry 4 to 5 minutes until the veg are lightly caramelized. Remove everything to a plate and set aside.

Add the fennel seeds to the pan and let them toast for 1 minute until fragrant. Add the pork, and use a spatula to break it up as it cooks. If the pan seems a little dry, add a little more olive oil. Once the meat's no longer pink, return the veg, onions and garlic to the pan. Sprinkle in a couple of pinches of salt and a few grinds of black pepper. Continue frying for 5 minutes, stirring occasionally, until the mixture's well-browned with some crispy bits.

Stir the wine into the pan and let it cook off for a few minutes until the meat is mostly dry again. Stir in the tomato paste and cook another 2 minutes. Deglaze the pan with the chicken stock, then add the canned tomatoes and throw in the sage. Turn the heat down to low and let simmer for 30 to 40 minutes until the sauce is reduced and thick. Check the seasoning and add more salt and pepper as needed.