Cook the Spinach: Heat 1 tablespoon of olive oil in a large skillet (preferably oven-safe) over medium heat. Add the garlic and cook for 1 minute. Add the spinach, salt, a dash of pepper, and a pinch of nutmeg. Cook, stirring, for 2 minutes or until the spinach is wilted. Remove the spinach to a plate and set aside. 

Sear the Chicken: Add 1 tablespoon each of olive oil and butter to the skillet and place it over medium-high heat. Pat the chicken with paper towels to dry and season on both sides with salt and pepper. Add the chicken breasts to the skillet (skin-side down if they have skin) and cook for 4 to 5 minutes per side, or until golden brown and the internal temperature reaches 165°F. 

Make the Sauce: Meanwhile, melt the butter in a saucepan over medium heat. Add the flour and cook, stirring, for 2 minutes. Whisk in the wine and cook for 30 seconds to deglaze, then stir in the broth. Cook for 2 to 3 minutes or until slightly reduced. Add the cream, Dijon mustard, and Parmesan cheese (if using). Taste and season with salt and pepper as needed. Continue simmering until smooth and thickened.

Assemble and Melt the Cheese: Top each chicken breast with a mound of wilted spinach and about 3 tablespoons of shredded Gruyère cheese.To melt the cheese, heat the broiler. Place the skillet 6 inches from the broiler element and broil for 1 to 2 minutes, or until the cheese is melted and bubbling. Watch closely. Alternatively, cover the skillet and place it over medium heat to melt the cheese.

Serve: Serve the chicken breasts over hot cooked linguine, angel hair pasta, or spaghetti. Drizzle with the creamy white wine sauce and enjoy!