Arrange the plastic shot cups on a baking sheet, keeping the lids off for now. This makes it easy to transfer them to the fridge later.

In a medium mixing bowl or a large liquid measuring cup, add the gelatin powder. Carefully pour in the boiling water and whisk continuously until the gelatin is fully dissolved and smooth.

Next, add the cold water and vodka to the mixture. Whisk again until everything is thoroughly combined.

Pour the liquid gelatin mixture into the prepared cups, filling each about three-quarters of the way to allow space for the lids once set.

Transfer the tray to the refrigerator and chill the shots for 2 to 3 hours, or until they are fully set and firm to the touch. Once set, snap the lids onto each cup and keep them refrigerated until ready to serve.