Bring 2 cups water to a boil in a large saucepan over medium-high heat. Remove from heat, and whisk in sugar and instant espresso, whisking until completely dissolved. Let cool 10 minutes.
Stir in vodka and, if desired, chocolate liqueur until well blended. Pour mixture into a 2-qt. glass bottle. Add vanilla bean. Cover tightly with lid, and shake thoroughly. Let stand in a cool, dark place 1 month, shaking at least once weekly.
Note: For testing purposes only, we used Godiva Original Chocolate Liqueur.