Pour 1 cup of the juice into a medium bowl. Sprinkle the gelatin evenly over the juice and sit for 10 minutes to soften.
Pour the remaining 3 cups of liquid into a saucepan and bring just to a simmer over medium heat. Remove from the heat, pour into the gelatin mixture, and stir to combine.
Chill:
Pour the mixture into a 9x13 inch baking pan, let cool, cover, and chill for at least 3 hours or preferably overnight.
Cut into shapes:
To serve, dip the bottom of the pan in hot water for about 10 seconds, then invert onto a cutting board. Using the large and small cookie cutters, cut out as many shapes as possible.
Notes
I have not tried this recipe with non animal sources of gelatin.