Preheat the oven to 425 degrees F.

Lay the pie crust out on a floured surface and roll thin. Transfer the crust to a pizza pan or cookie sheet lined with parchment paper.

Cut the rhubarb and berries into 1-inch slices. Sprinkle on the sugar and gently mix. Mix the flour and cornstarch in a small bowl with a fork. Slowly dust the fruit and place it in the center of the crust leaving a 2 inch edge around the fruit. Fold the crust up and over the edge of the fruit in a circular motion.

Whisk the egg and water and brush the egg wash on to the edge of the crust. Do not let it run under the crust.

Sprinkle with coarse sugar if desired.

Bake for 20 – 25 minutes watching so that the edge doesn’t burn.

Cool for 20 minutes and serve warm with ice cream or allow it to cool completely.

Slice into 4 generous servings and share with friends.