Mystery vegetable

[figment]

We joined a CSA, which means we get a share of vegetables every week. Last week, we got a bunch of salad greens and garlic and green onions and cauliflower and... this. I have no idea what it is. I assume it's edible.

What is this thing? How does one prepare/eat it?
ETA: Thanks! You are all very useful, and now I know I have a kohlrabi to eat tomorrow.