Pat dry and season.
Pat the salmon and shrimp dry with paper towels so they sear well.
Mix the Cajun blend in a small bowl.
Season the salmon on all sides and the shrimp generously. Reserve 1 teaspoon of the spice mix for the sauce.
Sear the salmon.
Heat a large skillet over medium-high. Add 1 tablespoon oil.
Place salmon in the pan (skin-side down if using skin-on). Cook 3–4 minutes until the edges look opaque and the crust forms.
Flip and cook 2–3 minutes more. Transfer to a plate; tent loosely with foil.
Sear the shrimp.
Add a drizzle of oil if the pan looks dry. Add shrimp in a single layer.
Cook 1–2 minutes per side until pink and opaque. Remove to the plate with salmon.
Build the garlic base.
Lower heat to medium. Add butter and olive oil to the skillet.
Stir in garlic; cook 30–60 seconds until fragrant. Do not brown.
Optional: Deglaze with a splash of white wine; simmer 30 seconds.
Simmer the sauce.
Pour in broth and scrape up browned bits.
Stir in heavy cream and the reserved Cajun seasoning. Simmer 3–4 minutes until slightly thickened.
Whisk in Parmesan until smooth. Add lemon juice to brighten.
Finish the dish.
Return salmon and shrimp (plus any juices) to the skillet.
Gently spoon sauce over the seafood and warm through 1–2 minutes.
Sprinkle with parsley and a pinch of red pepper flakes if you like extra heat.
Serve.
Serve over rice, pasta, mashed potatoes, or with crusty bread.
Add lemon wedges at the table for fresh acidity.
