HOW TO COOK MUSHROOMS
Cooking mushrooms is not difficult, although you have to follow certain guidelines to not make them look and feel out of order! Truly, the best thing to have are fresh mushrooms, but if you don't have ones you can use dry mushrooms after you've soaked them in hot water for 10-30 minutes and then drained off the water on a paper. Mushrooms are the perfect meaty food for vegetarians, and even if they can be eaten alone, they fit well together with meat or scrambled eggs or omelets.
Buying mushrooms
When you select mushrooms, or if you pick them on your own, look for the fresh, smooth, firm mushrooms. Avoid the ones that are sweaty, mushy, and obviously rotten. Dry mushrooms is another story, as you cannot judge how fresh they were when they were dried (unless they were really bad!). Make sure that you keep the fresh mushrooms refrigerated and use them within a few days of purchasing. Allow them to breathe, so no condensed water will form on their surface because then they will spoil quite quickly. Avoid freezing mushrooms! If you can't eat all of them at once then consider drying them. Just cut them into smaller pieces (not too small!), lay them out as a single layer on a paper, place a fan or two around it so the air is passed over the mushrooms and wait overnight. They should be dry then.
Preparation
To prepare mushrooms for cooking, you need to remove the hard fibrous parts of it. Usually the stalks are fine to use, but their ends (where the stem is attaching to the ground) may contain some unwanted threads, so cut them off and use them in some nice stock or sauce instead. You can also use the water that you used for soaking dry mushrooms in your stocks! Normally, the large part of the stalk can be used for cooking, with some exceptions, like shiitake mushrooms that may have hard chewy stalks.
Otherwise, you don't need to do much except cleaning them from the dirt and earth. The best way to do this is to brush the dirt off the mushroom. Sure, it may be more time-consuming than washing them with cold water, but the water can make the mushroom soggy. We don't like watery mushrooms, because when we cook them, we want to remove most of the water that's already there from the beginning. However, if you make the water rinsing a quick procedure, you can use this technique to remove the dirt. It is also a good idea to squeeze the water out of the mushrooms with your hand.
When it comes to peeling the skin, it's not necessary, but you may want to do this for purely esthetical reasons, if the dish you are making requires clean-looking mushrooms. Whatever your choice, you are now ready to cut slice the mushrooms into small cubes or slices, depending on your needs. For some dishes, mushrooms are mashed in a food processor, sometimes after they have been cooked.
Cooking/Sautéing
So what is the best way to cook mushrooms? Many chefs believe it's sautéing. Add a little oil to a medium-hot pan, let it warm up, and throw in your mushrooms but not too many at a time. They should turn red-brown after a couple of minutes, so then you flip them to the other side. Cook for another while until they get browned, and add some butter at the end of cooking to get more flavor (this is optional but tremendously flavor enhancing!). During the cooking, it is important to have a pan large enough so it will allow for a single layer of mushrooms, so the water they release will evaporate and not be taken up again. This is crucial so the mushrooms don't become mushy. The end result should be a brown, meaty, firm mushroom, and not a soaky, watery one.
Avoid aluminium pans when you cook white mushrooms, as the aluminium will discolor them.
It can be nice to have some seasoning in the pan together with the mushrooms, for example fresh thyme or rosemary, crushed garlic, or even a chopped onion. The aromatic molecules in these ingredients will be released into the oil and taken up by mushrooms, making them taste even better! After the mushrooms are cooked, taste them and add salt and peppar after desire.
Roasting/Grilling
Roasting the mushrooms is actually another good way to cook them, as you use dry heat that will help evaporate the water. Just lay the down in a pan, sprinkle with some oil, and put them in a hot oven until they become brown (about 20 minutes). Grilling mushrooms can be done by putting them on the grill rack, brushing with oil, seasoning, and grilling for a few minutes on each side, depending on the heat.
Mushroom aroma and additional aromas
Mushrooms have this wild-tasting aroma, and therefore they go well together with other "wild" ingredients. They are perfect for dishes that include meat from wild animals, but they are also nice on other types of meat (e.g. Beef Wellington). As mentioned above, more aromatics can be added to the mushrooms, for example, any aromatic vegetable that will release its flavory juices into the oil that the mushroom will pick up. So, onion, garlic, carrot, leek, and a lot of herbs can be used together with mushrooms.