Preheat the oven to 400°F (200°C).
Pat the salmon dry with paper towels and season both sides with salt and pepper.
In a large oven-safe skillet over medium heat, add 1 tablespoon olive oil.
Sear the salmon, skin-side up first, for 3–4 minutes per side until golden. Transfer to a plate.
To the same skillet, add another tablespoon of olive oil and the chopped shallot. Cook until softened.
Add garlic and butter. Stir until the butter melts. Sprinkle in the flour and cook for about a minute.
Pour in the cream and chicken broth, whisking constantly to avoid lumps.
Stir in Parmesan, Dijon, and red pepper flakes. Let the sauce thicken for a minute or two.
Add spinach and cook until wilted down into the sauce.
Return the salmon to the pan, nestling it into the creamy spinach sauce.
Transfer the skillet to the oven and bake for 10–12 minutes or until the salmon is cooked through.
Serve with a squeeze of lemon and your favorite crusty bread or rice.