Add the pudding mix and milk to a large mixing bowl, and whisk until combined.
Pour in the limoncello and whisk for 2 minutes until the pudding thickens.
Add one 8-ounce tub of Cool Whip to the bowl and fold it into the pudding until there aren't any streaks left. Put the bowl in the fridge for 5 minutes.
Lay out 28 plastic cups on a baking sheet. Add 3 tablespoons of the pudding mixture to each cup. Cover the cups with their lids and chill in the fridge for at least 1 hour.
Serve as is or pipe the remaining Cool Whip on top of each shot in a swirl. Serve immediately or chill until ready to serve.
Notes
Any leftover shots should be kept covered in the fridge for up to 5 days. You can also freeze them for up to 3 months. These shots are even good frozen!