Combine all of the ingredients except for the bitters in a cocktail shaker. Shake for about 20 seconds until frothy. Add ice and shake for another 20 seconds until thoroughly chilled. Strain into a chilled glass. Drop four drops of bitters around the top with an eye dropper and drag a toothpick through the center of each drop to create a swoosh. (Or just add a few dashes of bitters to the top of the drink and call it good.)