Bake shells according to package directions, and cool to room temperature.
Meanwhile, combine the pomegranate and blueberry juice 2 tablespoons sugar and lime juice in a saucepan over medium heat and bring to a simmer.
Mix the cornstarch with 1 tablespoons cold water to dissolve and whisk it into the juice, stirring until it returns to a simmer and thickens. Stir in the blueberries and half the lime zest. Remove from heat and set aside.
On a bowl, mix the ricotta, sour cream, remaining sugar and vanilla until smooth. Divide the ricotta mixture among all tart shells. Top each with the blueberry mixture and garnish with a pinch of the remaining lime zest, if desired.
Chill 10-15 minutes until set, or refrigerate overnight in airtight container.