Fiddlehead ferns, so named for the shape they grow into, are a delicious addition to your spring vegetable repertoire. Similar in flavor to asparagus, with a slightly bitter finish akin to broccoli rabe, they have a wonderful texture and bite to them and have become something I look forward to each year.
Before you dive head-first into a patch of sprouting ferns, there are a few bits of information that will be beneficial to you.
Some fiddlehead ferns are classified as 'toxic' and supposedly the ostrich fern is the least so. The general consensus is that they can cause gastrointestinal upset if too many are eaten. I haven't had problems with them, though, so I feel that the ostrich ferns are just fine. Go easy if you're trying them for the first time just to be on the safe side.
One thing you don't want to do is forage for them yourself unless you are very skilled at foraging. Look at Whole Foods or local farmers' markets during the month of May and you will likely find decent specimens. They can sometimes come with a sort of covering on them that resembles very fine garlic skin, but brownish in color. Simply give them a good rinse in clear water and you should be good to go.
Although they can be eaten raw in salads, I've not done so, preferring the change of texture once cooked. If you boil them, do so for 5 to 8 minutes only, any longer renders them mushy and flavorless. I like them sauteed in butter and garlic with a bit of sea salt and a squeeze of lemon juice, but I've also had them in a quiche with ham and cheese. Gently coddled by the cooking egg and cream, they are kept from overcooking and still have a nice crunch not unlike that of a lightly cooked fresh green bean.
Whatever you do with them, don't limit yourself - they are really something everyone should try once and I promise you it's worth it.