One of the easiest and most delicious ways to cook shiitake mushrooms is in a sauté pan, with a little onion and garlic. You will want to sauté the onion and garlic first in some olive oil until the onion begins to get soft. You can use a yellow onion, thinly sliced or diced, and either fresh or "jarred" minced garlic.
Slice the shiitake mushrooms thinly and add them to the pan. Cook until they get soft, approximately 10 or 15 minutes. You can serve over rice or pasta, or as a nice accent to chicken, shrimp, fish, you name it.
For the grill enthusiast in you, you can BBQ shiitakes quite easily. Leave the mushrooms whole and drizzle a little olive oil (spread over the entire mushroom) and salt to taste. Put them on the grill for about 5 minutes, flipping once.
You can also bake shiitakes in the oven in a covered pan for about 25-20 minutes. To steam them, add 2-3 tablespoons of water in the pan with them. You can add a little salt and olive oil if you like, or any other seasoning.
Shiitakes can also be used as a base for stock. Cut them into thick pieces and sauté them in a stockpot with yellow onions (diced) and garlic. Add about 2 quarts of water and cook on low heat for a minimum of 2 hours. Just like with any type of stock, the more you cook it down, the more flavor it will have.
Shiitake mushrooms are so versatile and compliment so many things, that it would be silly for you not to keep them on your grocery list on a regular basis. Even folks who are not fans of the "garden variety" shroom have found that they really enjoy shiitakes because it's such a distinctly different flavor.
So whether it be for the versatility, health benefits or robust, rich flavor shiitake mushrooms offer, you can not go wrong regardless of how you decide to incorporate them into a meal. Bon Appétit!