Mix the berries, lemon juice, sugar and corn starch in a large bowl. Set aside in the refrigerator.
Mix together salt and flour.
Using your fingers, quickly incorporate the butter with the flour mixture until it resembles coarse bread crumbs. (Don't form a paste, or allow the butter to melt.)
Drizzle 2 tbsp of the cream over the crumb mixture. Use your fingers to incorporate, it should be damp and hold together when pinched. Add more cream if necessary.
Transfer the dough to your baking sheet. Start from the center and pat the dough out to resemble a large rough circle.
Spoon the fruit mixture into the center of the dough, leaving about 2 inches around the edges.
Fold the edges up around the fruit, overlapping the edges.
Bake for 20-25 minutes until crust is just starting to brown.
Allow to cool completely before cutting. Serve with whipped cream or ice cream (optional).
You can use a premade pie crust if you like. I used a mixture of blackberries, raspberries, strawberries, and blueberries. Optional: Brush the outside of the crust with an egg wash or leftover cream for a touch of color.