Line a 9x9-inch square baking dish with plastic wrap, letting it hang over the sides of the pan; set aside.
Combine the water and mint leaves in a small saucepan and bring to a simmer. Remove from heat, cover, and let steep for 15 minutes.
Using a slotted spoon, remove the mint leaves from the saucepan and discard. Bring the water to a boil. Meanwhile, empty the Jell-O packets into a large bowl.
When the water comes to a boil, pour it over the Jell-O in the bowl. Stir with a wooden spoon until it has completely dissolved. Stir in the bourbon and lime juice. Pour the mixture into the prepared pan and refrigerate until set, 1 to 2 hours.
Using the plastic wrap "handles", lift the square of Jell-O out of the pan. Use a sharp knife or pizza cutter to slice into squares. Garnish with mint leaves, if desired. Refrigerate leftovers.
Notes
Note: If you prefer a Mint Julep Jell-O shot that does not include lime, check out the recipe at The Friday Football Foodie.