Add gelatin powder to a small mixing bowl. Pour 1/4 cup cold half-n-half of the powder and stir once to combine. Let sit until gelatin is dissolved.
Meanwhile, heat the half-and-half in a small saucepan over medium high heat until hot, but not bubbling.
Pour the hot liquid over the gelatin while whisking. Stir until the gelatin has melted.
Whisk in the sugar until dissolved. Add in the whiskey and creme de menthe; stir to combine.
Pour jello the plastic ramekins until almost full, just under the top line. (You want to leave room for the cherry and lid.)
Chill for 20 to 30 minutes until the jello begins to set up a little. Add a cherry to each ramekin, and chill until the jello is completely set, about 2 hours.
If you don't want the cherry juice to bleed into the shots, rinse and dry them before putting them in your shots.
If you want your cherry stems to stand up, you can place a piece of foil over the top of your ramekins, poke a hole in the foil over the center of each ramekin, and then pull the cherry stem through each hole. It's some work, let me tell you. Option B is to use stemless cherries. :)