1 1/3 cups tonic water
1 tablespoon lemon or lime juice
1 tablespoon sugar
3 envelopes plain Knox gelatin (makes a firm jelly shot for setting in a mold. Decrease to 2 or 2 1/2 envelopes if using other methods to set, such as loaf pan or mini martini glasses. An envelope of plain Knox gelatin equals about 2 tsp of gelatin powder.)
2/3 cup vodka (citrus flavored is nice . . .)
1 First, prepare the silicon molds with a light application of cooking spray. Then wipe the mold cavities out with a clean paper towel. This method will leave just the slightest residue, which will help unmold the gelatin without affecting the taste or appearance. Place each mold on a cookie sheet or cooling rack to provide a stable surface for handling.
2 Combine the tonic, citrus juice, and sugar in a small saucepan and sprinkle with the gelatin. Allow the gelatin to soak for a minute or two. Heat over low heat, stirring constantly, until gelatin is dissolved, about 5 minutes. (Mixture will be very foamy, but this will diminish.) Remove from the heat and stir in the vodka.
3 Pour the gelatin mixture into the molds, and refrigerate until fully set, several hours or overnight.
4 To serve, unmold, loosen the edges by pulling away from the side of the mold, and pop each jelly shot out.