Pat the salmon dry and season with the salt and pepper.
Heat the oil in a large skillet over medium-high heat. Sear the salmon for 3–4 minutes per side, until golden. Move it to a plate.
Reduce the heat to medium. Melt the butter in the same skillet, add the garlic and cook for 30 seconds, until fragrant.
Pour in the cream and stir in the Parmesan. Simmer gently for 2–3 minutes, until slightly thickened.
Add the spinach and cook for 1–2 minutes, until wilted.
Return the salmon to the pan and simmer for 2 minutes, until heated through and the fish flakes easily. Serve with the sauce spooned over the top.