In a 1-quart glass jar, combine the brandy, vodka, vanilla pods and seeds, and vanilla extract, if using. Place the lid on the jar and let the mixture sit in a cool, dark place for at least 3 months. [Editor's Note: The optional vanilla extract boosts the flavor quickly, but it’s by no means necessary. Another way to intensify the vanilla flavor is to save vanilla pods whose seeds you've scraped for another recipe and occasionally toss them in the jar.]