Cook pasta according to package directions. Reserve ½ cup pasta water before draining. Set cooked pasta aside.
In a large frying pan over a medium heat melt the butter and add the garlic, cooking for about 2 minutes until the garlic is frangrant. Add the sundried tomatoes and cook for a further 1 minute.
Add milk, stock and cheese, stir and bring to the boil (about 5 minutes). Allow to simmer for 15 minutes or until the cheese is all melted and the sauce starts to thicken up.
Add pasta and spinach and cook for 2-3 minutes until the pasta is heated through and the spinach is wilted. Add the pasta water if the sauce needs thinning out.