Thaw raspberries at room temperature 30 minutes. Using rolling pin, gently mash raspberries in sealed bag.
To make tarts: Heat oven to 425 F. Line baking sheet with parchment paper and set aside.
Place strainer over medium bowl; strain crushed raspberries 10-15 minutes, allowing juice to fall into bowl. Reserve juice for glaze.
In medium bowl, combine drained crushed raspberries and cornstarch; mix to combine.
Roll out both pie crusts into rectangular shapes and cut each into eight 2 1/2-by-4-inch rectangular pieces. Place rectangular pieces on prepared baking sheet. Add 1-2 TB crushed raspberris to center of each piece and top each with second rectangular piece. Use fork to crimp edges of dough.
Bake 10 minutes, or until crust is golden brown. Remove pastries from oven and allow to cool completely.
To make glaze: In medium bowl, whisk powdered sugar, reserved raspberry juice and vanilla. Drizzle on cooled pastries and garnish with sprinkles