Spray cups or molds lightly with cooking spray. (Skip this step if using lime shells.)
In a small saucepan over medium heat, combine sugar and water. Stir until sugar dissolves. Do not boil. Remove from heat.
Add the lime juice to a medium bowl. Sprinkle gelatin over top and allow to rest for 5 minutes until gelatin is softened and the liquid’s surface appears slightly wrinkled.
Stir the lime-gelatin mixture into the sugar water. Warm over medium heat for 2 to 3 minutes, stirring until gelatin is completely dissolved. Do not let boil. Remove from heat. Stir in the tequila and triple sec.
Distribute the liquid evenly among the molds. Refrigerate 3 to 4 hours before serving. If using lime shells, cut in half to create lime wedges before serving.
Notes
If you wish to use margarita mix, add 1 ½ cup sour mix to a saucepan. Sprinkle gelatin over the top, then wait 5 minutes until the surface is wrinkled. Then warm the mixture for 2-3 minutes until the gelatin has dissolved.If desired, rim the edges of the shot glasses in sugar or salt. Rub a lime around half the edge of the cup and then roll it in kosher salt or granulated sugar.For top-shelf margarita jello shots, use top shelf tequila and Grand Marnier instead of triple sec.