In a blender, combine whiskey, cream, condensed milk, eggs, chocolate syrup, and coconut extract (if using). Blend until smooth.
Serve chilled, over ice.
Notes
*In place of chocolate syrup, use 2 teaspoons sugar, 2 teaspoons cocoa, and ¼ teaspoon vanilla
Hand mixer method: Beat eggs until frothy. Add whiskey, cream, condensed milk, chocolate syrup, and coconut extract if using, and mix until smooth. Refrigerate for up to one month, stirring before using.
Store for two weeks in the refrigerator. Shake well before use.