The most potent, albeit the most expensive, way to add vanilla flavor is with the whole bean. Inside each long, leathery, dark-brown pod you'll find thousands of tiny black specks bursting with vanilla flavor. The seeds not only add intense flavor but also a visual element. Vanilla beans are especially handy for infusing liquids with vanilla flavor, such as when making custards.
One 2-inch piece vanilla bean = 1 tsp. extract
Pure vanilla extract can be used in place of vanilla beans, but in cases where the beans are being steeped in a boiling liquid, such as cream, add the extract off the heat; otherwise its flavor dissipates.
The perfect bean is 5 to 7 inches long, plump, and has very dark brown skin; it should feel moist and supple (not dry and brittle) when rolled between your fingers. And be sure it passes the sniff test: Even through heavy plastic, the aroma should be close to intoxicating. The flavor of the vanilla beans is affected by where they're grown. In general, Madagascar beans, which is what you're most likely to find, are sweet and buttery, and the beans are long and thin. Tahitian vanilla is known for its fragrant and floral aromas; and Mexican vanilla, which is shorter and plumper, tastes nuttier.
If you're making a custard or otherwise infusing a liquid with vanilla, throw both the seeds and the pod in the pot. If you're adding vanilla seeds to a batter and you want to be sure they're distributed evenly, take a small bit of the batter, smush the seeds into it until they're thoroughly mixed in, and then fold this concentrated vanilla portion into the rest of the batter. To remove the seeds: Hold the bean down on either end. With the tip of a paring knife, poke a hole in the top and slide it down the bean, splitting it in half lengthwise. Open it with the knife tip and scrape down, collecting the seeds on the blade.
Vanilla beans will dry out and become brittle if left out in the air, so wrap them in foil, seal them in a zip-top bag, and store them in a cool, dark area. They'll last this way for at least several months. If they begin to dry out, add them to your vanilla extract or a jar of vodka. And once you've scraped the seeds from a pod, don't discard it: The pod still has tons of flavor. Add it to your sugar container, coffee beans, or favorite liqueur.