Pies can be a tricky thing to bake. They require a long time in the oven, the filling can become (and stay) runny, the crust can burn quickly, and once they’re “done,” it’s almost impossible to know how everything will look and taste until the first tell-tale slice is cut. I’ve had a lot of luck with recipes in the past (blueberry and peach versions come to mind), and this one is another safe bet (the hint of cinnamon sends the taste over the top, like a really good jam). My best advice is to make sure the filling actually hits its boiling point–that way you know the cornstarch has activated and will set as it cools. Also, taste the mixture you stir together before you seal the pie. It’s your last chance to adjust for sweetness and spices!
For the crust: Mix 2⅔ cup flour with 1 teaspoon salt in a bowl. Pour ⅔ cup oil into a measuring cup. Add 6 tablespoons milk. Do not stir. Pour liquids into the flour and salt mixture and mix briefly until dough comes together. Do not refrigerate. On a lightly floured surface, roll out dough to a ⅛-in.-thick circle. Transfer to a 9-inch pie plate. Trim crust to ½ inch beyond rim of plate. Roll out remaining dough scraps, cut into desired patterns, and set aside.
For the filling: Preheat oven to 400°. Whisk sugar, cornstarch, salt, water and cinnamon in a saucepan until smooth. Bring to a boil. Add blueberries. Cook and stir 2 minutes or until thickened. Cool slightly.
Add filling to pie crust. Arrange remaining cut dough over filling. Brush with milk and sprinkle with coarse sugar. Bake 50 minutes to 1 hour, or until crust is golden brown and filling is bubbly. Cool on a rack and serve.