To make the crust, combine the flour, salt and sugar in a food processor; add the butter and pulse until the mixture resembles coarse meal.
Add the sour cream and water; process a few seconds until a dough ball just starts to form (do not over-process).
Note: to make the dough by hand, place ingredients in a mixing bowl and use a pastry blender to cut butter and shortening into flour mixture; add the sour cream and ice water, and just mix until it comes together and forms a mass.
Transfer the dough to a floured work surface and pat down to about 1-inch thick.
Cut into 2 pieces; wrap each one in plastic wrap, and refrigerate for at least 30 minutes, or overnight.
To make filling, coarsely grind the orange in a food processor or blender; set aside.
In a large saucepan, mix together all remaining ingredients, along with orange, stirring to combine, and bring to a boil.
Reduce heat to a simmer and cook, stirring constantly, until mixture thickens and sugar is dissolved, about 4-6 minutes; set aside to cool completely.
Position the rack in the center of the oven, and the other rack just beneath it.
Peheat oven to 400 degrees F.
To prepare pie, roll out 1 piece of the dough on a slightly floured surface into a circle about 12-inches in diameter (dust surface with more flour as necessary).
Roll the dough around the rolling pin, lift it over a 10-inch pie pan, and unroll over the pan; adjust to center the dough, then press into place.
Roll out the remaining dough into a 12-inch circle; spoon the cooled filling into the pie shell in the pan, mounding it in the center.
Using a pastry brush dipped in the milk, moisten the sides of the bottom crust, then drape the top crust over the pie.
Lightly press the top and bottom crust edges together, and trim the excess dough by running a knife around the edge of the pan.
Crimp edges to make a decorative border; also cut 3-4 venting slits in the top crust to allow steam to escape.
Brush top crust with milk, and sprinkle with turbinado sugar.
Place the pie in the preheated oven, and place a rimmed baking sheet below it.
Bake for 45- 50 minutes, or until the crust is golden brown.
Cool on a wire rack; serve warm or at room temp; goes well with ice cream.