Set your oven to 400°F and lightly grease a 9x13 baking dish with oil or nonstick spray.
Season the chicken thighs generously with Italian seasoning, salt, and pepper.
Heat 2 tablespoons of butter in a large skillet over medium-high heat and brown the chicken skin-side down for 2 to 3 minutes on each side; then remove from heat.
Add the remaining tablespoon of butter to the same skillet, toss in the spinach, and sauté, stirring now and then, until it softens, about 2 minutes; remove from heat.
Arrange the chicken pieces in a single layer in the prepared baking dish, then layer the halved potatoes and cooked spinach over the chicken.
Prepare the garlic parmesan cream sauce: melt ¼ cup butter in the skillet over medium heat, stir in garlic and cook until fragrant, about 1 to 2 minutes.
Whisk in flour and cook, stirring constantly, until it turns a light golden color, roughly 1 minute.
Gradually pour in chicken broth, adding thyme and basil, whisking continuously to incorporate, about 1 to 2 minutes.
Stir in half and half and Parmesan cheese, cooking until the sauce thickens slightly, 1 to 2 minutes; add extra half and half if the sauce is too thick and season with salt and pepper.
Pour the prepared sauce evenly over the chicken, potatoes, and spinach in the baking dish.
Place the dish in the oven and bake until the chicken is cooked through and reaches an internal temperature of 165°F, about 25 to 30 minutes.
Once cooked, sprinkle chopped parsley on top for garnish and serve immediately.