If you're cooking something that requires boiled cabbage leaves, such as Eastern European stuffed cabbage, you needn't boil it. As my cousin Millie told me, stash the cabbage heads in the freezer ahead of time, until they are frozen through, probably two days before you need the leaves. Then remove them and let them thaw, maybe a day before you need them. The leaves should pull away from the core easily.
The freezing and thawing softens the leaves just as boiling them would, only better. "Your cabbage-freezing cousin is a genius," my friend told me after executing this process. "I have never gotten so many leaves off of a head of cabbage ever before, and I didn't have to cut out the ribs." She's right.