Bend each vanilla bean until it cracks open slightly. Place all the vanilla beans in the jar. Add glycerin and water. Shake to mix. Let sit for a few weeks in a cool, dark place. When ready, use like regular vanilla extract.
You can reuse the vanilla beans by refilling the jar with glycerin and water. The beans should last for some time. When the vanilla flavor begins to lose intensity, add a fresh vanilla bean to the extract.
Adapted from PetitChef at http://en.petitchef.com