Preheat oven to 400F.
Roll out one homemade gluten free pie crust pastry according to linked recipe.
Combine sugar, gfJules Flour, water and salt in a small saucepan and stir over medium heat until boiling. Continue to cook 2 more minutes while stirring. Mixture should be clear and thick; do not cook until mixture browns.
Remove from heat and whisk in butter, lemon juice, lemon zest, cinnamon and nutmeg. Add 2 cups blueberries and let cool down to warm. Then gently stir in remaining 4 cups blueberries.
Meanwhile, transfer bottom crust in a 9-inch pie pan. Fill with blueberry filling.
Roll out and transfer second crust. Crimp edges or press with the tines of a fork to seal the two crusts.
Brush top pastry with egg wash or milk. Sprinkle with cinnamon and sugar, if desired. Cut a few slits in the top crust (or use a small cookie cutter to cut small holes in the top crust) to let steam vent during baking. Cover edges of crust with foil or crust protectors to prevent over-browning.
Place pie in preheated oven and bake 15 minutes. Reduce heat to 375 F, remove foil and bake an additional 35 to 40 minutes or until juices bubble and pie is lightly browned.
