Step 1

Pulse fennel, onion, and fennel seeds in food processor until finely chopped, about 10 pulses, scraping down sides of bowl as needed; transfer to separate bowl. Process tomatoes in now-empty processor until smooth, about 10 seconds; transfer to second bowl. Pulse sausage in now-empty processor until finely chopped, about 10 pulses, scraping down sides of bowl as needed.

Step 2

Heat oil in Dutch oven over medium-high heat until shimmering. Add sausage and cook, breaking up meat with spoon, until all liquid has evaporated and meat begins to sizzle, 10 to 15 minutes.

Step 3

Add fennel mixture and 1/2 teaspoon salt and cook, stirring occasionally, until softened, about 5 minutes. (Fond on bottom of pot will be deeply browned.) Add tomato paste, garlic, and oregano and cook, stirring constantly, until fragrant, about 30 seconds.

Step 4

Stir in wine, scraping up any browned bits, and cook until nearly evaporated, about 1 minute. Add 1 cup water and pureed tomatoes and bring to simmer. Reduce heat to low and simmer gently, uncovered, until thickened, about 45 minutes. (Wooden spoon should leave trail when dragged through sauce.) Season with salt and pepper to taste; cover and keep warm.

Step 5

Bring 4 quarts water to boil in large pot. Add pasta and 1 tablespoon salt and cook, stirring often, until al dente. Reserve 1 cup cooking water, then drain pasta and return it to pot. Add 3 cups sauce and 1⁄2 cup reserved cooking water to pasta and toss to combine. Adjust consistency with remaining reserved cooking water as needed. Transfer to serving dish. Drizzle with extra oil, sprinkle with Parmesan, and serve. (Remaining 3 cups sauce can be refrigerated for up to 3 days or frozen for up to 1 month.)