I planted my cauliflower too close together. If I thin it out can I cook the greens? The plant are about a foot+ tall

Yes. Just like broccoli greens, try to harvest the younger, more tender leaves. Tastier and less bitter.

Wayne

Yup - in fact all the brassica greens are edible, although some are better than others.

Personally my favorites are broccoli & kohlrabi leaves - but as AG just said, the smaller the better.