Preheat oven to 425°.

Combine peaches, raspberries and lemon juice in a medium bowl and set aside.

In another bowl, combine granulated sugar, instant tapioca, and cinnamon. Stir into the fruit mixture and let stand for ten minutes.

Unroll pie crust onto a parchment-lined baking sheet or pan.

Spoon filling onto the center of the crust, leaving at least 2 inches around the edge for folding over.

Fold the edge over the filling, pleating as you go with your fingers.

Use a pastry brush to brush egg whites over the folded over edges of the pastry crust.

Slice butter into thin squares and dot the filling.

Sprinkle filling with coarse sugar.

Bake on baking sheet in oven for 25 - 30 minutes, or until the crust is golden brown and the filling is cooked through.

Transfer the crostata to a wire rack to cool for at least ten minutes before serving.