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, can add 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.