I've made this recipe for years. I think it was from an early 1980's Canadian Living Magazine.
4 cups fresh blueberries
3/4 cup sugar
4 tablespoons all-purpose flour
1/2 tsp cinnamon (optional)
2 tablespoons melted butter
1 tablespoon lemon juice
pastry for double crust
Line pie plate with pastry.
Mix together blueberries, 3/4 cup sugar, flour and cinnamom (if using) and melted butter; pour into pie crust. Cover with pastry and cut a few slashes in top; or cut pastry into strips and prepare lattice top. Seal edges well and flute. Brush lightly with milk and sprinkle with
sugar. Bake in 425°F oven for 15 minutes, reduce heat to 35o°F and bake about 40 minutes longer or until crust is golden.