Toast the hemp seed hearts: Preheat oven to 300 degrees. Spread hemp out on baking sheet and toast for 15 mins on the bottom rack. Stir around once. Cool completely.
Add hemp seed hearts, flour, Xylitol sugar, and salt in a blender and pulse to combine.
Add the cold butter pieces and pulse until crumbly.
Add ice water, one tablespoon at a time, and the vanilla extract, and process until dough forms a ball around blade. Don't overprocess.
Remove the dough and wrap in parchment paper and chill for 30 mins.
Place the berries in a large bowl.
In a small bowl, stir together the sugar and flour.
Toss the mixture into the berries and stir gently.
Place a rack on the second slot from the top; Preheat oven to 375 degrees.
Turn the pastry dough out on a floured surface and roll the dough into a 16-in circle using a floured rolling pin.
Folded dough in half.
Gently transfer the dough into the 10-in cast iron skillet, then gently unfold, fitting it into the bottom of the skillet, allowing excess pastry to hang over the edge of skillet. Doesn't have to be perfect.
Spoon in the berry mixture with most of it in the middle.
Fold over the edges of the pastry dough up around the berry filling, overlapping when necessary so the juices won't escape.
Now, whisk together the egg and water. Brush on top of the pastry.
Sprinkle pastry with the turbinado sugar.
Bake 35 to 40 minutes. The pastry should be golden brown and the fruit hot and bubbly
Let cool for 1 hour to set the juices and serve warm.