Method
Strain the blueberries:
Strain the blueberries in a colander or fine-mesh strainer over a large liquid measuring cup. Add enough water to the syrup in the measuring cup to total 4 cups of liquid.
Heat the liquid and add the Jell-O:
Pour the liquid into a medium saucepan. Bring the liquid just to a simmer over medium heat, then remove the saucepan from the heat. Add the Jell-O to the saucepan and stir continuously until the mixture is completely smooth, with no granules of gelatin remaining, 1 to 2 minutes. Pour the mixture into a medium mixing bowl.
Make an ice bath and partially chill the Jell-O:
Add a few cups of ice cubes to a large mixing bowl, then pour in a few cups of tap water. Gently lower the mixing bowl with the Jell-O mixture into the bowl of ice water—the water should come about halfway up the side of the smaller bowl.
