In a saucepan over high heat, bring 1 cup water to a boil. Meanwhile, place the jello in a large glass measuring cup or bowl.
Pour the boiling water carefully into the jello and stir until the jello is disolved. Stir in vodka.
Pour the jello mixture into disposable 2-ounce portion cups or shot glasses, and refrigerate until set, about 2 hours.
Jell-O: Any 3-ounce flavor of Jello will work for this recipe, so choose a flavor you enjoy and a color that matches the color scheme.
Vodka: The subtle spirit plays nicely in these shots. See note 8 for other liquor ideas.
Yield: Each 3-ounce box of Jello makes 10 Jello Shots.
Two hues: For shots with 2 color layers in one cup, fill shot glasses halfway with the first Jello mixture and refrigerate for 2 hours. Repeat with the second color and refrigerate until set, about 2 hours more.
Make ahead: Prepare up to 3 days in advance, then store in airtight containers in the refrigerator for 3 to 4 days.
Sugar-free: If desired, substitute one 0.6-ounce box of sugar-free Jello for the 3-ounce box of regular Jello.
Gelatin sheets: To prepare Jello Shots using gelatin sheets instead of powder, mix together 1 cup vodka and 1 cup fruit juice, such as lemon juice. Add 2 (230 bloom strength) gelatin sheets and allow to bloom for 10 minutes. Meanwhile, make simple syrup in a small saucepan by mixing together 2/3 cup of water and 2/3 cup granulated sugar. Bring to a boil and remove from heat. Whisk hot simple syrup into the gelatin mixture. Continue with step 3. If fresh fruit juice is used, the Jello shots may take longer to set up.
Other liquors: If you're not fond of (or don't have) vodka, substitute in spirits you enjoy. Consider cocktail-inspired mixes: Try tequila and lime Jello for a Margarita Jello Shot, bourbon and orange Jello for an Old Fashioned Jello Shot or gin and lemon Jello for a Tom Collins Jello Shot.