Blueberry Lattice Pie

Prepare and chill the dough.
To make the filling, combine 1 cup of the blueberries with the sugar in a nonreactive saucepan.
Bring to a simmer over low heat, stirring occasionally, until the sugar is melted and the mixture is very liquid about 5 minutes.
Combine the cornstarch and water in a small bowl and whisk the blueberry and sugar mixture into it.
Return everything to the pan and cook, stirring constantly, over low heat, until the mixture comes to a boil, thickens and becomes clear.
If it does not become clear, continue to cook over low heat for a few more minutes, until it does.
Pour into a large bowl and stir in the remaining filling ingredients, except the blueberries, then add the remaining 3 cups blueberries.
Cool.
Set a rack at the upper and lower thirds of the oven and preheat to 400F (200C).
Roll out the bottom crust and arrange in pan.
Pour the cooled filling into the bottom crust.
Prepare a lattice top crust.
Flute the edge of the pie and carefully brush it with egg wash.
If you wish, sprinkle the top of the pie with sugar.
Place the pie in the oven on the lower rack and reduce the temperature to 375F (190C).
Bake for about 40 minutes, until the crust is baked through and a deep golden brown and the filling is gently bubbling.
If the top crust has not colored sufficiently after 30 minutes of baking, move the pie to the upper rack of the oven for the last 10 minutes.
Cool the pie on a rack.