In an 8-cup, microwave-safe, spouted measuring cup, add 2 cups of water and microwave on high for 4 minutes to boil the water. Add 2 of the (0.25-ounce) packets of unflavored gelatin to the hot water and whisk until completely dissolved. Whisk in the sweetened condensed milk and ½ cup vodka until completely smooth, and the sweetened condensed milk is thinned out. Divide this mixture into three equal portions (approximately 1½ cups each). Set aside to cool.
In a 2-cup, microwave-safe spouted measuring cup, add 1 cup of water and microwave on high for 3 minutes. Sprinkle in 1 (0.25-ounce) packet of unflavored gelatin and whisk until completely dissolved. Add 1 (3-ounce) box of raspberry-flavored gelatin and whisk to combine. Finally, add ¼ cup of vodka and whisk to combine.
Pour the raspberry gelatin into a thin layer on the bottom of a 9x13 glass baking dish. Carefully transfer to a flat surface in the refrigerator and allow it to chill and set up for 45 minutes.
Once you have finished preparing your first raspberry (red) layer, then you will want to wash your measuring cup and prepare your lime (green) layer so that it has time to cool off on the counter, before adding it to the layers of holly jolly jello shots. You DO NOT want to add hot or warm jello to the dish of layers because it can melt the layer you are pouring it onto, thus ruining the layered look of the holly jolly jello shots.
Prepare your lime (green) gelatin by following step 2, except you will replace the raspberry with the lime gelatin. Set aside to cool off once mixed. You will repeat this step after making each layer alternating between raspberry and ending with the lime. Make sure to wash your measuring cup between flavors.
Once your raspberry layer has chilled and set up, carefully pour on one of your (1¼ cup) portions of the sweetened condensed milk mixture. Place the dish back into the refrigerator to chill and set up for 45 minutes.
Add your pre-mixed lime (green) gelatin mixture. Chill for 45 minutes.
Make your second (3-ounce box) raspberry (red) layer and set it aside to cool on the counter.
Add the second 1¼-cup sweetened condensed milk mixture (give it a quick stir before pouring if it has started to firm a little, so you don’t have lumps). Chill for 45 minutes
Carefully pour on the premade raspberry layer. Chill for 45 minutes.
Make your final (3-ounce) box of the lime (green) mixture and set it aside to cool on the counter.
Add the final 1¼-cup portion of the sweetened condensed milk mixture to the dish. Chill for 45 minutes.
Pour on the final mixture of lime-flavored gelatin. This will be your top layer. At this point, you will want your holly jolly jello shots to have a good amount of chill time. I highly suggest an overnight chill in the refrigerator, but a minimum of 6 hours is needed to really make sure that all of the layers have set up and are firm.