Season thighs with salt and pepper. Sear in olive oil over medium-high heat until golden, 5–6 minutes per side; remove and set aside.
Reduce heat, add butter and onion; cook until soft. Stir in garlic and sun-dried tomatoes, cook 1 minute.
Pour in broth and cream, then add Parmesan and Italian seasoning; simmer until slightly thickened.
Return thighs to pan, spoon sauce over them, cover and cook 12–15 minutes until internal temp reaches 165°F.
Stir in spinach to wilt, garnish, and serve with sauce spooned over.