After last time's impassioned discussion about rice, on to an even more sticky subject (at least if you get it right).
I have never been terribly fascinated by the chemistry of cooking; I am generally happy enough to get results without worrying too much about explaining the process by which they are reached. But one rather general point has always been clear to me: most cooking is about making raw food easier to chew. That is why we soften vegetables and pasta by boiling them, and why we generally prefer cooked meat to raw (for those of us who eat it at all).
However, there is a large range of exceptions, and the biggest is the opposite process - making a liquid go thick. There is still something pretty magical about it for me: basic science tells us that if you heat something, eventually you will melt it, yet here the opposite takes place. There are two basic recipes I use all the time which do this: scrambled eggs and white sauce.
I remember as a sixth-former being surprised when one of my friends mentioned scrambled eggs as his favourite snack to cook. But, y'know, he had a point. It is one of the simplest recipes out there, but the output looks very different from the input and tastes very gratifying. It is astonishingly simple. Crack as many eggs as you want (one or two per person) into a pan; add a dash of milk (as much as you would put in tea or coffee) per egg, and the same amount of butter if you like; also add salt and pepper. Then mix it all together (using either a whisk or a wooden spoon) to form a pale yellow viscous mixture (the butter, if you used it, does not need to be integrated as it will melt). Then start heating (on medium if you can take your time, top if you are hungry), and keep stirring. Within a couple of minutes, the egg simply cooks - there is a school of thought that you can turn the heat off once it starts to thicken, but you have to keep stirring. I like to eat it on hot buttered toast, with a sprig of parsley on top if one is available.
Less simple, but also basic for a lot of other good cooking, is the recipe for white sauce/bechamel sauce/roux. When making a fairly thick sauce for pasta, I use roughly 25g (2 tablespoons in US) of both flour and butter and 200 ml (half a US pint) of milk per person. You can't use coarsely ground flour, and it is easier if you use very finely ground flour; I imagine you can use margarine etc instead of butter with obvious consequences for the taste. Other variations on the basic technique use other liquids than milk (most often stock, which for me means hot water with a stock cube dissolved in it).
First, melt the butter in a saucepan. Then, take it off the heat and add the flour, and stir until it has all gone sticky. Then add the liquid - my technique is to add first small amounts and try and keep consistency with vigorous wooden spoon action; there is also a school of thought which just adds all the liquid and keeps whisking. Once all the liquid is in, add salt and pepper, put it back on the heat and put the heat back on, and keep stirring (again, I am a wooden spoon man, but I suppose other implements can be used). After a few minutes - say five - it should miraculously thicken up, and it is ready (often benefits from a couple more minutes standing off the heat).
I like to throw in a handful of grated cheese once it has thickened; and then pour it onto my pasta (or vegetables - broccoli, for instance). Other versions include a pinch of nutmeg or arrowroot. The basic technique is fundamental to many other recipes. I have become so instinctive about it that I no longer measure out the ingredients and simply judge the amounts by eye; it usually works.
The biggest problem with both scrambled eggs and white sauce is that they require your almost undivided attention for the few crucial minutes of cooking. It is therefore tricky to combine them with other similarly demanding recipes, such as stir-frying; or with other attention-seeking distractions, such as hungry small children. But that is really a matter of planning. (And the children, once old enough, can help stir the pan.)