01 -
Strain the blueberries using a fine-mesh strainer over a large liquid measuring cup. Add enough water to the collected syrup to total 4 cups of liquid.
02 -
Pour the liquid into a medium saucepan. Heat over medium heat just to a simmer, then remove from heat. Stir in the gelatin mix until fully dissolved and smooth, about 1 to 2 minutes. Transfer to a mixing bowl.
03 -
Create an ice bath by filling a large bowl with ice and cold water. Place the bowl with gelatin mixture into the ice bath so water comes halfway up the outside of the bowl. Stir every few minutes until the mixture is lightly gelled but not firm, about 30 minutes, reaching approximately 45 to 55°F.
04 -
Remove the gelatin mixture from the ice bath. Fold in the sour cream and strained blueberries gently until fully combined, allowing streaks to remain if needed.
05 -
Pour the mixture into a 10.5-cup gelatin mold or bundt pan. Tap gently to level and cover with plastic wrap. Refrigerate for at least 8 hours or overnight until fully set.
06 -
To unmold, dip the mold into warm water for about 10 seconds, then invert onto a serving plate. If it resists, repeat dipping and gently loosen edges with an offset spatula or butter knife to release suction before flipping again.
07 -
Slice the gelatin using a cake server and plate individual portions. Serve immediately. Cover leftovers tightly and refrigerate up to 3 days.