Once you make your own homemade vanilla extract you will be ruined to the store-bought stuff! It's so easy to make, but you do need to have patience. The longer it sits, the better it gets. You'll need to wait at least 5 weeks to crack into the bottle. I use 18 vanilla beans for a 750ml bottle of vodka.
If you are using the whole vanilla beans, scrape out the pulp of a bunch of beans.
Put the pod and scraped pulp into the bottle. (Scraping out the pulp first will help it flavor the alcohol quicker.)
Pour the vodka into the bottle. You can use a funnel to make sure you don't spill. I didn't have one that was small enough, so I used a large round pastry tip.
Close the stopper on the bottle and shake the vanilla and vodka to distribute the seeds. The vodka will still be clear for the first few days. Once every couple of days give the extract a good shake to break up the pulp and get the seeds distributed in the vodka. After a week the extract will start to get darker and develop some flavor. After two weeks you can use the extract, but the flavor will be very subtle.
At week 3 the color should be amber and the aroma is richer, but waiting for week 4 or 5 is when it gets really exciting. Use it in any recipe that calls for vanilla extract. If you are using it in buttercream, you may want to strain out any of the pulp. You will still have the seeds in your recipe, but any of the stringy bits from the pod will get strained out.
Refilling the vanilla extract: As you use the vanilla, you can add more vodka and vanilla beans to refill it and keep it going for years. After I've scraped the seeds from a bean for a recipe, I just toss the bean into my bottle and shake it up. If your bottle gets to be half empty and you refill it with vodka, you will want to add a few more beans to make sure you're not diluting it too much.
The extract can be kept indefinitely and over the months it just keeps getting better.