Boil the pasta according to the packet instructions.
Heat the butter in a large frying pan over a low heat. Add the garlic and fry lightly for 2 minutes. Add the flour and whisk until smoothly combined with the butter. Heat for a further two minutes before adding the stock, 50mls at a time, whisking well after each addition. Repeat with the milk. Stir through the cheese until it melts and then the cooked pasta. Add the spinach, stir until lightly wilted. Serve topped with fresh parsley, black pepper and more cheese if you wish.