A sweet, crunchy biscuit crust, filled to the brim with fresh wild blueberries. A perfect end of summer treat.
Preheat oven to 375F and grease a large 12 inch cast iron pan (or a large, deep glass dish) with butter. In a large bowl, mix together the flour, baking powder, baking soda, salt and 1/4 cup sugar. Using pastry blender or two knives, cut the butter into the flour mixture until you have small pea sized bits of butter and it's well mixed together. Place bowl in freezer, until ready to use.
Whisk the buttermilk and 1 egg together in a separate bowl, set aside. In another bowl, mix the blueberries with the flour and sugar, stir well to coat the berries.
Remove flour/butter mixture from freezer, and add the wet ingredients, mixing gently with a fork until just combined. Form dough into a round disk and turn out onto a well floured surface. Pat the dough together and using a rolling pin, roll out into a 1/4 inch thick circle.
Using your rolling pin, grab one side of the dough and gently roll it onto your rolling pin to transfer to the pan. Add the berry mixture to the center of the dough and carefully fold up the edges around the berries.
Whisk an egg and brush the edges of the dough with the egg. Sprinkle egg wash with sugar, then transfer to the oven, cover with aluminum foil and bake for 60-75, you want the blueberries to start bubbling in the center. If the dough has not browned under the foil after 60 minutes, remove foil and bake uncovered for remaining time. Let cool 15 minutes before serving with vanilla ice cream, if desired.