1. Split 1 vanilla bean, and scrape seeds into a clean 1/2-pt. jar. If desired, cut bean in half crosswise. Place in jar. Repeat procedure with remaining beans and 2 (1/2-pt.) jars.
2. Cook bourbon in a large saucepan over medium heat 5 minutes. (Do not cook longer than 5 minutes or it can overheat and ignite.) Pour 1 cup bourbon into each jar. Cool mixture to room temperature (about 30 minutes).
3. Cover jars tightly, and let stand at room temperature 1 to 2 weeks before using, shaking jars once a day. (For a cleaner look, pour liquid through a fine wire-mesh strainer into clean bottles with tight-fitting lids; discard solids.) Store in a cool, dark place up to 1 year.
Note: When cooking alcohol, be sure to use a large saucepan to contain vapors. Do not heat longer than 5 minutes--the vapors can ignite. The vodka version has the purest vanilla flavor. Though both extracts turn a rich brown after 1 week, the bourbon version is slightly darker.