In a large glass bottle that can hold 48 ounces liquid, pour vodka and bourbon.
Cut vanilla beans in half. There is no need to split or scrape out the vanilla as the alcohol will extract it. Place all 40 vanilla beans in bottle and shake. Place in cool, dark area and shake every couple of weeks. You want in dark area, as light will dilute the vanilla aroma. The longer it sits, the better the vanilla. I'd recommend at least 6 months or up to a year.
Once ready, clean and sanitize the 4 oz bottles. I recommend using amber bottles so the vanilla aroma stays and lasts! You can add a label and give as gifts!
Alternatively if you don't have a big glass bottle you can just place 3 vanilla beans in each bottle and pour 3 ounces of vodka and 1 ounce bourbon. Keep in dark place for 6 months and label when ready.
No need to go expensive with the alcohol. Use cheap 80 proof alcohol.
If you prefer bourbon, you can use more bourbon than vodka.
Use Grade B vanilla beans as they're cheaper and meant for extracting.
Keep the ratio of 5-6 vanilla beans per 8 oz of alcohol for the best quality vanilla extract.
For best quality, have your vanilla extract sit for at least 6 months in a dark area.