Commercial vanilla extract usually has simple syrup (sugar water) added to the extract to give it a sweet aftertaste. You can do this if you want, but if you are using the vanilla for baking, there really is no need.
Method
1 Use kitchen scissors or a sharp paring knife to cut lengthwise down each vanilla bean, splitting them in half, leaving an inch at the end connected.
2 Put vanilla beans in a glass jar or bottle with a tight fitting lid (mason jars work well). Cover completely with the vodka.
3 Give the bottle a good shake every once in a while. Store in a dark, cool place for 2 months or longer.
Lasts for years. You can keep topping it off with vodka once in a while as you use it, just remember to give it a good shake.
You can also make vanilla sugar by putting a split vanilla bean into a jar of white, granulated sugar. Great way to infuse the sugar with vanilla flavor for baking.