This is a 700ml bottle of vanilla extract. Well, it will be.
Take one bottle of vodka. Split one or more vanilla beans & insert in bottle. Screw lid on tightly. Put in the back of the cupboard for 6-8 weeks.
That's it. The longer you leave it, the stronger the vanilla extract will be.
You can also re-use vanilla beans that you've used for something else (rinse well before adding to the alcohol), and you can use other alcohols that aren't too strongly flavoured themselves. You can 'feed' it by adding more vanilla beans as you go, and top it up with more alcohol. Neverending vanilla extract ...