Bring a large pan of salted water to the boil. Trim the leaves from the cauliflower; discard only the gnarly outer leaves. Cut the cauliflower into small florets, and stem into similar sized pieces.

Cook the spaghetti in the water according to the pack instructions. At the same time, put a frying pan over a medium-high heat. Add 20g butter; when it starts frothing, tip in the cauliflower florets and stems and cook for 8-10 minutes on a medium- high heat until golden, stirring occasionally.

When the spaghetti is 1 minute away from being done, add the thicker cauliflower leaves into the pasta water. Add the remaining butter, 6 tablespoons of pasta water and black pepper to the cauliflower pan. Stir to form a sauce. 

Drain the spaghetti and leaves, reserving a little more of the cooking water. Return them to the pan, sprinkle the Parmesan over the top; add the florets and thinner cauliflower leaves, making sure the cauliflower is well distributed. Add a spoon or two of cooking water if necessary. Leave the pasta to relax into its sauce for 1 minute before serving in warmed bowls.