Bring a large pot of salted water to a boil. Cook fettuccine noodles a few minutes shy of al dente, according to package directions. The noodles will finish cooking in the sauce.
Pat salmon filets dry and salt and pepper each side. Heat a large skillet over medium-high heat and add olive oil. Add the salmon filets, skin side down if they have the skin on, and sear for 4 minutes. The salmon should pretty easily lift up when it's ready to flip, if not, give it another minute. Sear on the other side for 3-5 minutes until the internal temperature reaches approximately 145°F. Remove from pan and set aside.
In the same skillet, add butter. Once melted, add the sliced shallots and a pinch of salt; cook for 2-4 minutes until slightly soft. Add minced garlic, a pinch of salt, freshly ground black pepper, and red pepper flakes if using. Cook for 2 minutes, then add the corn kernels and cook for an additional 3-4 minutes. Stir in pesto, milk, and 1/4 cup pasta water, and additional salt to taste; bring to a simmer.
Stir in parmesan cheese and add in the just-before-al-dente noodles; toss to combine, adding additional pasta water as needed to reach the desired consistency of the sauce. Taste test for salt levels, too. Let the noodles cook for an additional 1-2 minutes in the sauce.
Serve with salmon filets or flake the salmon and toss in the pasta.
Be sure to pat the salmon dry completely before pan-searing to get a wonderfully seared crust.If using half-and-half, you may need to add additional pasta water to the sauce to loosen it up.Don't forget to salt along the way and taste test levels! The parmesan will add additional salt to the pasta, so I recommend salting a little less than normal before adding, and being sure to taste test once the cheese is in and adjusting from there.