01 - Pat the salmon fillets dry with paper towels and season both sides evenly with 1/2 teaspoon salt and 1/4 teaspoon black pepper.
02 - Heat olive oil in a large skillet over medium-high heat until shimmering. Add salmon fillets skin-side down if using skin-on. Sear for 4 minutes until golden, then flip and cook for 2-3 minutes until almost cooked through. Remove salmon from skillet and set aside on a plate.
03 - Reduce heat to medium. Add butter to the same skillet and let it melt. Add minced garlic and diced onion, sautéing for 2-3 minutes until fragrant and translucent.
04 - Stir in sliced sun-dried tomatoes and cook for 1 minute to release their flavors.
05 - Pour in heavy cream and broth, using a wooden spoon to scrape up any browned bits from the bottom of the pan. Bring the mixture to a gentle simmer.
06 - Add Parmesan cheese and Italian seasoning. Stir continuously until the cheese melts completely and the sauce thickens slightly, about 2 minutes.
07 - Add baby spinach leaves and cook for 1-2 minutes until just wilted. Taste and adjust seasoning with additional salt and pepper if needed.
08 - Return salmon fillets to the skillet, spooning sauce generously over each piece. Simmer gently for 2-3 minutes until salmon is cooked through and sauce is creamy and cohesive.
09 - Transfer to serving plates immediately, garnished with fresh basil leaves and lemon wedges if desired.