WALNUTS
Walnuts grow on trees of Juglans regia, well hidden and protected in their shells that need to be broken in order to get your hands onto the brain-like two-lobed edible part of the nut. There are actually a number of variants of walnuts, but there is pretty much only one dominant sort that has been enjoyed around the world since ages. Walnuts are consumed in large amounts nowadays, being only second most high after almonds. They are praised not only for their flavor, but also for the nutritional values - they have large amounts of omega-3 oils (which normally are found in seawater fish). The aroma of a walnut is very much based on its oils and the molecules that are dissolved in it, and you can also find walnut oils in the stores, if you want to add some walnut-like flavor to your dressings and vinaigrettes. Walnut oil have also been used to produce the so called walnut milk, which is widely used in some cultures around the world.
Other uses of walnuts include pickled walnuts - the immature green nuts that still have their soft shells are picked from the trees, usually in June, and soaked in salt water for several days, after which they are dried. Now the walnuts have turned their color to dark brown or black, and can be preserved in a pickling solution which may be sugary, spicy, or just made of vinegar. The same green walnuts can also be stored in syrups, something that is practiced in the Middle East. Yet another way to use them is to flavor other liquids, e.g. alcohols (vin de noix).
Some other types of walnuts, or rather relatives to the popular Juglans regia are available. Juglans nigra for example is a black walnut, which is smaller and more flavorful, although it is hard to handle. Another variant, Juglans cinerea, is a very tasty nut but is for some reason not that famous.
When you buy walnuts, the best and only season for them is the fall, since this is when they mature to the brown hard-shelled nuts. Make sure though that once you crack the nut and have the 'flesh' exposed, to not keep them in the light and heat for too long time. The reason is omega-3. Even if it is a good nutrient for your body, it becomes rapidly rancid when exposed to light and heat, pretty much like butter does. Instead, store opened nuts in darkness and in cold (a refrigerator is okay), or even better - don't crack the nuts until you are about to consume them. You can see how the nuts become bad by how rubbery and shrinking they become. This is good to know if you prefer buying shelled walnuts, which I personally dislike. The magic about unshelled walnuts is that you can store them in cold and darkness for a long time, even up to 6 months, which should be enough until a new season starts again.
Walnuts are successfully paired with cheeses of many sorts, but are particularly good with Roquefort, or with Stilton. This combination can be used in many recipes, whether it is an appetizer, a salad, or a dessert you are creating. Other ingredient combinations for walnuts include raisins and caramel, on the sweet side, and mushrooms, zucchini, and cepes on the savory side. You can also try to mix walnuts with pork or with fish. To make things more exciting, try using pickled walnuts and see how they blend with all these ingredients.