Strictly speaking, you probably won't need to cook those frozen crab legs you purchased at the supermarket or at the discount club store--it has already been done for you. You will just need to heat them up. Make sure you do it properly, though, by following these tips.
You must first thaw the crab legs. Allow them to thaw in your refrigerator overnight; don't make the mistake that many people do of thawing them at room temperature or, even worse, thawing them by zapping in a microwave oven. Thawing at room temperature is a bit risky from a food-safety standpoint , and microwaving can overcook crab legs.
Once the legs are completely thawed, then you can heat them in the microwave--or in a conventional oven. You can also steam or boil them.
Microwaving
Place crab legs in a microwave-safe pan or on a dish. Cover with a couple of thicknesses of paper towels and heat on high for 2 to 3 minutes.
Boiling
Fill a large pot 2/3 full of water. Add several shakes of salt and any other seasoning that you like. Bring water to a boil. Drop crab legs into the boiling water. Immediately reduce heat and let the pot simmer for 4 to 6 minutes.
Steaming
Fill a large saucepan with water and bring to a boil on stove. Place crab legs in a vegetable steamer or a colander and place over the pan. Allow the legs to steam for 4 or 5 minutes.
Heating in an Oven
Heat oven to approximately 420 degrees F. Place crab legs on a baking sheet and place in oven on a top rack. Roast for 4 or 5 minutes.
The best crab legs are king crab legs, but most types of crab sold for food have a good deal of meat in their legs and especially their claws. Sometimes there is more meat in the legs than in the body itself.
Crab legs are made up of three distinct sections. To get at the meat, just break the sections apart at the joints. Then take hold of one of the sections and press it with your thumbs on the flat side until the shell cracks. You should be able now to remove the shell and pull out a good-sized piece of meat. The claws will probably need to be cracked with pliers or with special tools available from kitchen specialty shops.
Cooked crabmeat straight from the legs is delicious by itself, or you can brush it with melted butter before eating. Crab leg meat is also good in any recipe calling for crabmeat generally.