Pie with berries

Ingredients     1 cup cherry preserves     1/4 cup sugar     3 tbsp cornstarch     225 gms blueberries     300 gms raspberries     2 tsp butter, cut into small pieces Preparation     Mix: Scrape preserves into a large bowl. Stir together sugar and cornstarch; sprinkle onto preserves; mix thoroughly.     Roll in all the berries. Add butter, and using a rubber spatula,mix gently. Line a baking sheet with parchment paper.     Set chilled sour-cream pie pastry on top. Pile fruit mixture into the pastry. Settle frozen lattice on top. Slide into a 2000C oven and bake until crust is light brown, 25 minutes.     Cover loosely with foil and continue baking until the crust turns golden brown and the juices bubble, 20-25 minutes more. Cool on a rack completely before demoulding and slicing.