Prepare the oven and baking dish. Preheat the oven to 350°F. Lightly coat a 2.5- to 3-quart baking dish with butter and set it aside.

Cook the broccoli. Pour approximately 1/2 inch of water into a large skillet, season the water with salt, and bring it to a boil. Add the broccoli florets, cover the skillet, and cook over high heat for 3 to 4 minutes, or until the broccoli reaches a crisp-tender consistency.

Drain the broccoli. Thoroughly drain the cooked florets, then transfer them directly to the prepared baking dish.

Prepare the creamy cheese mixture. While the broccoli cools slightly, place the softened, cubed cream cheese in a mixing bowl with the sour cream, shredded cheddar, grated Parmesan, minced garlic, Italian seasoning, salt, and black pepper. Stir until all ingredients are thoroughly combined and evenly incorporated. Allowing the cream cheese to reach room temperature helps it blend smoothly with the remaining ingredients.

Coat the broccoli. Spoon the prepared cheese mixture over the broccoli in the baking dish. Stir carefully but thoroughly until the florets are evenly covered with the creamy cheese mixture.

Bake the casserole. Place the dish in the preheated oven and bake for 17 to 20 minutes, or until the cheese mixture is bubbling and the top has developed a light golden-brown color.

Rest before serving. Remove the casserole from the oven and allow it to stand for approximately 5 minutes before serving. This brief resting period allows the mixture to settle and the flavors to meld.

Garnish. If desired, scatter crushed red pepper flakes over the casserole immediately before serving to provide a subtle touch of heat and color.