Prep the chicken: Pat chicken dry. Season both sides with salt, pepper, and 1 tablespoon of ranch seasoning. This builds flavor right into the meat.
Sear for color: Heat a large skillet over medium-high.
Add olive oil and 1 tablespoon butter. Sear chicken 4–5 minutes per side until golden. Remove to a plate; it doesn’t need to be fully cooked yet.
Soften aromatics: Reduce heat to medium.
Add remaining butter. Stir in onion and a pinch of salt. Cook 3–4 minutes until softened.
Add garlic and cook 30 seconds until fragrant.
Deglaze: Pour in chicken stock, scraping up browned bits. That fond is pure flavor. Stir in remaining ranch seasoning and a pinch of red pepper flakes if you like a little heat.
Make it creamy: Reduce heat to medium-low.
Whisk in heavy cream. If using cream cheese, add it now in small pieces and stir until smooth. Simmer gently 2–3 minutes to thicken slightly.
Return chicken to the pan: Nestle the seared chicken into the sauce.
Simmer 6–8 minutes, flipping once, until chicken is cooked through and the sauce is silky. Internal temperature should reach 165°F.
Finish the sauce: Stir in Parmesan until melted. Add lemon juice to brighten.
Taste and adjust salt and pepper. If using spinach, fold it in and let it wilt for 1 minute.
Serve: Garnish with chopped parsley or chives. Spoon extra sauce over the chicken.
Serve with rice, pasta, mashed potatoes, or roasted vegetables.