Prep the chicken: Pat chicken dry. Slice large breasts horizontally to create cutlets, or pound to an even 1/2-inch thickness. Season both sides generously with salt, pepper, paprika, and garlic powder.
Sear the chicken: Heat 1 tablespoon oil and the butter in a large skillet over medium-high heat.
Add the chicken and cook 4–5 minutes per side until golden and cooked through (internal temp 165°F/74°C). Transfer to a plate and tent with foil.
Soften aromatics: Reduce heat to medium. Add a drizzle more oil if needed.
Sauté shallot for 2 minutes until softened, then add garlic and cook 30 seconds until fragrant. Don’t let it brown.
Wilt the spinach: Add spinach in batches, tossing until it just wilts. If using frozen spinach, add it now, breaking it up and cooking off excess moisture.
Build the sauce: Pour in chicken broth and scrape up browned bits from the pan.
Stir in heavy cream, nutmeg, and a pinch of red pepper flakes if using. Simmer gently 2–3 minutes to thicken slightly.
Melt in the cheese: Reduce heat to low. Stir in parmesan until smooth.
Taste and adjust salt and pepper. If sauce gets too thick, loosen with a splash of broth.
Return the chicken: Nestle the chicken and any juices back into the skillet. Spoon sauce over the top.
Simmer 1–2 minutes to warm through.
Finish and serve: Add a light zest of lemon or a small squeeze to brighten the sauce. Garnish with chopped parsley. Serve straight from the skillet.