Bring a large pot of salted water to a boil.
Cook rigatoni according to package instructions until al dente.
Reserve 1/2 cup of pasta water, then drain and set aside.
Season salmon with salt and pepper.
Heat olive oil in a large skillet over medium heat.
Cook salmon 3β4 minutes per side, or until just cooked through.
Remove from skillet and flake into chunks using a fork. Set aside.
In the same skillet, melt butter over medium heat.
Add garlic (and shallot, if using) and sautΓ© until fragrant (about 1 minute).
Pour in white wine (or broth), scraping up any browned bits from the pan.
Simmer for 2β3 minutes until slightly reduced.
Reduce heat to low. Stir in the heavy cream, Parmesan, lemon zest, and red pepper flakes.
Simmer for 3β4 minutes until the sauce thickens slightly.
Add the cooked rigatoni and flaked salmon to the sauce.
Toss gently to combine, adding reserved pasta water a little at a time if needed to loosen the sauce.
Stir in lemon juice and fresh parsley. Taste and adjust seasoning.
Plate the creamy salmon rigatoni and garnish with extra parsley and Parmesan if desired.