Combine the milk and cream together in a bowl or some other storage container with a lid.
Pick, then coarsely chop the fresh basil leaves and add them to the milk and cream mixture along with the lemon peel. Seal the container and place it in the refrigerator overnight.
Next, pass the infused liquid through a strainer and into a sauce pot. Discard the basil and lemon peel.
Sprinkle the measured amount of gelatin onto the liquid and let it hydrate for a few minutes. Once the gelatin looks saturated go ahead and add the sugar and vanilla extract. Give the mixture a stir and warm it over low heat just until the sugar and gelatin have dissolved. To finish, whisk in the sour cream until the mixture is smooth.
Pour equal amounts of the liquid into multiple serving containers, then transfer them to the refrigerator so the panna cotta can set. This should take about two hours.
Let the panna cotta rest at room temperature for ten minutes before serving. Garnish each vessel with fresh blueberries and small basil leaves to complete the presentation.
Makes 4, 6 ounce servings