Instructions

1. Heat a Dutch oven or wide, extra-deep sauté pan over medium heat and drizzle the pan with a tiny bit of olive oil. Spread the oil around as the pan heats up. When the pan is hot, crumble in the raw sausage. Brown the sausage over medium to medium-high heat for about 10 to 15 minutes, stirring and scraping frequently. (Don't worry if a lot of sausage residue sticks to the bottom of the pan; this will get taken care of later.)
2. While the sausage is cooking, peel and finely dice the onion, and mince the garlic. Remove the stalks and fronds from the fennel and reserve the fronds for garnish later. Dice the fennel bulbs into a similar size and shape as the diced onion. (You may dice up the long stalks as well, but I find that they just don't get as tender in this recipe. I compost them, but you can add them if you like.)
3. When the sausage is browned and partially cooked in small crumbles, add the diced onion, garlic, and fennel. Stir thoroughly so the vegetables are coated with the sausage fat. Turn the heat down to medium-low and cook the vegetables with the sausage for at least 15 minutes, or until they are beginning to be tender.
4. When the vegetables are beginning to be tender, add the two cans of diced tomatoes and the tomato puree. Stir thoroughly and bring to a simmer over medium heat. Add the rosemary sprig, a pinch of salt, and a few grinds of black pepper. Lower the heat to a bare simmer, and cover the pot loosely with a lid. Cook for at least 1 hour, stirring occasionally.
5. After an hour, take off the lid and taste the sauce. It should have cooked down into a jammy, thick sauce with still-juicy bits of fennel and small chunks of sausage. It probably will not need more salt, as the sausage tends to be quite salty, and some canned tomatoes have salt added. But taste and adjust as needed.
6. The ragù can be refrigerated for up to five days, and frozen for several months (or more). It gets even better tasting after a night in the fridge.
7. To serve, ladle the ragù over freshly-cooked pasta and garnish with a sprinkle of chopped fennel fronds and a generous pinch of freshly grated Parmesan.