Using a sharp knife, split your vanilla beans down the middle so that the beans inside are exposed, then place into your glass bottle. If you beans are too long for your bottle, cut them in half so that they fit.
Pour you vodka or bourbon over top of the beans and make sure they are fully submerged in the alcohol.
You can start to use your vanilla extract in as little as 8 weeks but the flavor will be even better if you wait 6-12 months.
While you're waiting, store the vanilla at room temperature out of direct sunlight and give it a shake 1-2 times a week.
Notes
Once you start to use your vanilla, you can refill with a little more alcohol each time! Just give it a shake after adding more alcohol and before you use it! The most important thing is just making sure the beans are always fully submerged.As long as your vanilla is stored properly, it's good to use indefinitely! But if you're unsure just do the smell test. If it still smells good, it's good to use! If it ever started to smell rancid, toss it.You'll notice that the vanilla bean seeds start to settle in the bottom of the jar. Don't worry about those ending up in your baked goods, they just add extra flavor! (I personally love how the flecks of vanilla bean look in things like vanilla frosting).