For the Filling:

1. Place two cups of the blueberries in a large bowl. Add the coconut sugar, lemon juice, and arrowroot powder. With a large fork or masher, mash the berries slightly until some of the juices start to flow, and the mixture gets a little liquidy.
2. Add the chopped dark chocolate and the remaining 4 cups of the berries. Stir to coat the berries with the mixture. Set aside.

For the Assembly:

1. Set out a 9-inch pie pan.
2. For the bottom crust, roll out one pie round until it is slightly larger than your pan, with an extra 1/2-inch circumference around the pan. Use flour to prevent the crust from sticking as you roll. Transfer to the bottom of the pan pan. Press down on the bottom and sides, and cut any excess around the edges.
3. Add the blueberry mixture to the pie plate.
4. For the top crust, you can create a lattice effect with the top crust, or use the dough to cover the entire top of the dough. Use flour for dusting to prevent sticking. Crimp the edges, and remove any excess dough. If using the dough to cover the entire pie, use a knife to slice a small opening to allow steam to escape.
5. Use any scraps of dough for extra decorations.
6. Let the unbaked pie chill in the refrigerator for at least 30 minutes, or up to 1 hour. As the pie is chilling, preheat the oven to 350°F.
7. Remove the pie from the fridge. Brush the top crust with the milk, and evenly sprinkle the sugar on top.
8. Bake for 60 to 75 minutes, until the crust is a light brown color and you can see the filling lightly bubbling.
9. Remove from the oven and let cool slightly for 20 minutes before serving warm. To serve cold, let the pie cool completely at room temperature, and place in the refrigerator to cool and set for at least 4 hours.