The following items offer some challenges in the kitchen. Here's how to know when they are done cooking.
For creamy, intact beans, turn off the heat before the beans are fully cooked. Cover the pot and let residual heat continue to soften the interior without any agitation from boiling water, which can rupture delicate skins.
Most egg dishes provide visual cues when done, but not hard-cooked eggs. To keep that greenish ring from forming around the yolk, bring large eggs to a boil in a pot of water, turn off heat, cover, and let them sit for exactly 10 minutes before transferring them to a bowl of ice water to stop the cooking process.
Forget about trying to judge color when toasting nuts. When the nuts are fragrant, they are done.
Properly cooked pasta will have a slight bite (that is, it will be al dente). If in doubt, cut a piece in half. If you see a white core, the pasta needs more time. Many recipes suggest simmering the drained pasta in the sauce to help marry the two; if you plan on doing this (a good idea for many cream and broth-based sauces), undercook the pasta slightly.
Potatoes and other root vegetables are generally done when a skewer slides through them and meets little resistance. With peeled potatoes, the pieces should just break apart when pierced with a skewer or paring knife. When boiling whole potatoes, try lifting them out of the water with a paring knife; if the potato clings to the knife (even for an instant), it's not done yet.
It's not hard to make rice tender; fluffy rice is another matter. Rather than continuing to cook the rice and risk scorched or blown-out grains, place a folded kitchen towel between the pot and the lid and then set the covered pot aside for 10 minutes. Residual heat will continue to steam the rice while the towel absorbs the excess moisture.