Slice the lemons in half lengthwise, from stem to end. Carefully scoop out all the pulp from each lemon half. Be gentle to avoid piercing the rind. Squeeze the pulp through a fine-mesh strainer to get your 1/4 cup of fresh lemon juice. Set the juice aside.
Place the hollowed-out lemon rinds snugly into the cups of a muffin tin to hold them steady.
Make The Lemon Drop Jell-O Mixture
In a small bowl, pour the 1/4 cup of fresh lemon juice. Sprinkle the packet of unflavored gelatin evenly over the top. Let it sit for 5 minutes without stirring.
In a separate bowl, empty the packet of lemon-flavored Jell-O. Pour the 1 cup of boiling water over it and whisk until the powder is fully dissolved.
Add the unflavored gelatin mixture to the hot lemon Jell-O. Whisk continuously until the gelatin has also completely dissolved and there are no clumps or grains remaining. Stir in the chilled vodka and chilled triple sec and mix well.
Fill, Chill, And Slice
Carefully pour the liquid Jell-O mixture into the hollowed-out lemon rinds in the muffin tin, filling them to the brim. Transfer the muffin tin to the refrigerator. Let the Jell-O shots chill for at least 4 hours, or until completely firm. Overnight is best.
Once set, place one lemon half, cut-side down, on a cutting board. Slice each half into 2 or 3 wedges.