Place the granulated coffee, water, sugar, and one split vanilla bean into a large pot, heat on low until the sugar dissolves. Bring to a low boil. Stir occasionally until the coffee crystals have dissolved. Coffee foam will float to the top of the mixture.
Remove the pot from the heat and allow to cool to room temperature. Once cool, skim off as much foam as possible. Pour the vodka into a large glass jar. Split the two remaining vanilla beans and add them to the glass jar.
Pour the coffee syrup into the jar. Gently stir with a large spoon to combine. Place a tight fitting lid on the jar.
Place the jar in a cool dark cabinet and steep for 4 to 6 weeks before using. Steeping longer allows for richer flavor.