Lightly spray your shot vessel with non-stick cooking spray. (I used a silicon 1-ounce ice cube tray, but you can also use a mini muffin tin, plastic ice cube tray, or even a sheet pan.) Wipe out any excess collected spray with a paper towel.
In a small saucepan, combine the ginger beer and lime juice. Sprinkle the gelatin over the surface of the liquid and let it sit for 5 minutes to “bloom.” Basically, it will soften and form a film on the top of the liquid that looks sort of wrinkled.
Warm the mixture over medium-low heat for 1-2 minutes, stirring constantly until the gelatin is fully dissolved. Do NOT let the mixture boil, people!!! If you’re unsure whether or not the gelatin is dissolved, rub the liquid between your fingers. If it feels slipper and smooth with no grains of gelatin, it’s done.
Remove from the heat and stir in the vodka.
Pour the liquid into the prepared shot vessel (I recommend using a measuring cup with a lip to make things easier), and refrigerate for 4 hours or overnight until set completely.
To remove the shots, use a thin knife to slice around the edges of each shot and press them out of the mold. (You can also invert the mold and run a little warm water over it to help loosen them, if you’re having trouble.) Refrigerate until ready to serve.