Preheat oven to 375 degrees F.

Using pastry cutter or food processor, cut butter to size of large peas.

In large mixing bowl, combine flour, sugar, salt and butter. Slowly drizzle in buttermilk and incorporate well with fork. If needed, use hands to gently fold dough until it comes together completely and feels sticky.

Once sticky, press dough into disc shape and cover with pastry cloth or plastic wrap. Chill in refrigerator for 20 minutes.

In large mixing bowl, combine berries, sugar, tapioca starch and almond extract and let sit for 10 minutes to macerate.

Flour surface and roll out dough into large, ½-inch thick circle. Transfer to baking sheet lined with parchment paper.

Arrange filling in center of dough, avoiding excess liquid released from fruit; leave 2-3 inch border.

Fold edges of crust toward center, leaving filling exposed. Sprinkle on cinnamon.

Whisk egg and brush over crust, then sprinkle with sugar.

Bake for 45 minutes or until crust is golden brown.

Cool for 20 minutes before serving. Top with mint leaves or ice cream, if desired.