Add the dry spaghetti to a large pot and pour in the broth. Bring to a boil over medium-high heat, stirring occasionally, until the pasta is just tender and the liquid has reduced to a creamy sauce, about 10 minutes.
Reduce the heat to medium and add the butter to the pot. Stir until melted and the garlic is fragrant, about 1 minute. The garlic should soften and release a warm aroma.
Gradually sprinkle in the grated parmesan cheese, stirring continuously to help it melt into the sauce, creating a smooth and velvety coating over the pasta.
Season the dish with salt and black pepper to taste. Stir well to incorporate the flavors evenly.
Cook for an additional 2-3 minutes, stirring occasionally, until the sauce thickens slightly and the pasta is glossy and well-coated.
Turn off the heat and give the pasta a final stir. Serve hot directly from the pot, topped with extra parmesan if desired and a sprinkle of fresh herbs.