Bring a large pot of salted water to a boil. Cook the rigatoni according to package directions until al dente. Reserve 1/2 cup of pasta water before draining.

While the water heats, heat olive oil in a large skillet over medium-high heat. Add the sausage meat, breaking it into small bite-sized chunks with a wooden spoon. Cook until browned and crispy, about 6-8 minutes.

Reduce heat to medium. Add the thinly sliced fennel bulb and minced garlic to the pan with the sausage. Sauté for 5-6 minutes until the fennel softens and begins to caramelize.

Pour in the white wine to deglaze the pan, scraping up any browned bits from the bottom. Simmer for 3 minutes until the liquid reduces by half.

Lower the heat and stir in the heavy cream and chopped sage. Simmer gently for 4-5 minutes until the sauce slightly thickens. Season with black pepper and a pinch of salt (be careful as sausage is salty).

Add the cooked rigatoni and half of the Parmesan cheese to the skillet. Toss vigorously to coat the pasta, adding a splash of reserved pasta water if the sauce looks too thick.

Serve immediately, topped with the remaining Parmesan cheese and garnished with the reserved fennel fronds.