Special equipment: a 10- to 12-ounce bottle with a tight-fitting top
Split the vanilla beans lengthwise, leaving them attached at one end. Place them in a 10- to 12-ounce bottle and cover with the liquor. Put on the top and shake vigorously. Store at room temperature for 4 weeks to let the flavor develop and mature, shaking the bottle once a week. The extract will keep at room temperature in a dark place (like your cabinet) for up to 6 months.