01 - Pat the salmon fillets dry with paper towels. Season both sides generously 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. Place salmon fillets skin-side down (if using skin-on) and sear for 4 minutes until golden. Flip carefully and cook for 2-3 minutes more until almost cooked through. Transfer to a plate and set aside.
03 - Reduce heat to medium. Add butter to the same skillet and let melt. Add minced garlic and diced onion, sautéing for 2-3 minutes until fragrant and translucent, being careful not to burn the garlic.
04 - Stir in sliced sun-dried tomatoes and cook for 1 minute to release their oils and intensify flavor.
05 - Pour in heavy cream and broth, using a wooden spoon to scrape up any browned bits from the bottom of the pan. Bring to a gentle simmer.
06 - Add grated Parmesan cheese and Italian seasoning. Stir continuously until cheese melts completely and sauce thickens slightly, about 2 minutes.
07 - Add baby spinach leaves, tossing until just wilted. Taste sauce and adjust seasoning with additional salt and pepper as 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. Serve immediately, garnished with fresh basil leaves and lemon wedges if desired.