They're basically baby cabbages. If you didn't eat cabbage directly, you've likely had it in egg rolls, sauerkraut, or coleslaw. It's that hearty green texture with a little sweet leafy flavor especially if you get leafier ones.
I broil them halved in a deep glass pan (to hold in some moisture) with butter, bacon, onions, garlic, heavy on the coarse black pepper and salt. Maybe even tomato and shrimp. Just let it go until they are chewable but firm mixing as the leafs char slightly.