Gelatin: Soak the gelatin according to the package instructions, usually 8–10 minutes. If using powdered gelatin, sprinkle it over 2 tablespoons of cold water and let it bloom for 5 minutes.3 ¼ gelatin sheets
Blend the blueberries with 1 tablespoon of sugar and set aside.⅔ cup blueberries + 1 tablespoon granulated sugar
Heat the cream: In a saucepan, heat the cream, sugar, and vanilla extract or scraped vanilla bean over medium heat until it just starts to boil. Remove from heat.2 cups heavy cream + ¼ cup granulated sugar + 1 teaspoon vanilla extract
Add gelatin: Add half of the blended blueberries and the lightly squeezed gelatin leaves (or bloomed powdered gelatin). Stir until the gelatin is completely dissolved.
Divide the mixture between 4 small dessert jars or glasses. Refrigerate until set, at least 4 hours or overnight for the best results.
Serve: Top the panna cotta with the reserved blended blueberries and decorate with some fresh blueberries, if desired.
Notes
Gelatin: I use 4 gelatin sheets, a total of ≈0.25 oz (6.7 g). In the US, this equals 3 ¼ sheets of gelatin. You can also use about 2 teaspoons of powdered gelatin (Knox) in the US.
Blueberries: You can use fresh or frozen (then defrosted) blueberries - both work well. For decorating, fresh berries look nicest on the panna cotta.