Start by slicing the fennel bulb very thin.
Remove the tough core first.
Dice the onion into small pieces.
Mince the garlic cloves finely.
Remove sausage from casings if using links.
Having everything ready makes cooking much easier.
Bring a large pot of salted water to boil.
Add the rigatoni pasta to the boiling water.
Cook according to package directions until al dente.
This usually takes about 10-12 minutes.
Drain the pasta but save one cup of pasta water.
Set the pasta aside.
Heat olive oil in a large skillet over medium-high heat.
Add the sausage to the hot pan.
Break it into small pieces with your wooden spoon.
Cook until the sausage is browned all over.
This takes about 6-8 minutes.
Remove the cooked sausage and set it aside.
In the same skillet, add sliced fennel and onion.
Cook these vegetables until they're soft and golden.
This takes about 8 minutes.
Add the minced garlic and red pepper flakes.
Cook for one more minute until fragrant.
Don't let the garlic burn.
Pour the white wine into the skillet.
Let it bubble and reduce by half.
Add the crushed tomatoes to the pan.
Return the cooked sausage to the skillet.
Stir everything together well.
Let the sauce simmer for 10 minutes.
Add the heavy cream and stir gently.
Add the cooked rigatoni to the sauce.
Toss everything together until pasta is coated.
If the sauce seems too thick, add pasta water.
Stir in the grated Parmesan cheese.
Season with salt and pepper to taste.
Garnish with fresh basil before serving.