There’s an easier way. Cut the whole head into quarters first, and then angle the knife to cut out the cores. Note that the cauliflower cores and leaves are perfectly edible; the cauliflower cores are much like broccoli cores. If you want, peel them and slice them for snacks, or chop them and cook them the way you would the florets. You can chop the core and leaves and cook them along with the florets.
