Mix everything, minus the whiskey, together in a blender until smooth.
Slowly add the whiskey, in small amounts, incorporating it completely before adding more. (Apparently, adding it too fast can make it curdle. We didn't test to confirm this...but better safe than sorry!)
Store in an airtight container for up to 1 month in the fridge.
This recipe makes a fairly large batch. We made a half batch and it was just a bit too much for our 12 ounce bottle.