For the crust, place flour in food processor. Add sugar and salt and process for 20 seconds to combine. Add butter and shortening and pulse until crumbly. Drizzle lemon juice and ice water on top. Turn on processor for 15 seconds or until mixture holds together.
Turn out dough onto lightly floured work surface. Knead gently for a few seconds until dough is smooth. Seperate the dough in half and pat into two flattened disks. Wrap well in plastic and chill dough for 1 hour or overnight.
When ready to make the pie, preheat oven to 425ºF. Remove dough from refrigerator. Between two sheets of plastic wrap, roll out both disks of dough to fit a 9-inch pan. Place one piece of dough in pan, leaving excess dough to crimp crust later.
In a large bowl, add cranberries, apples, raspberries, blueberries, strawberries, and rhubarb. Add sugar, flour, and cornstarch, and stir to thoroughly and evenly coat fruit. Place fruit in prepared pie crust, making a mound in the middle.
Place second piece of rolled out dough over fruit. Crimp crust as desired. Make air vents with paring knife. Brush pie top and crust with milk and dust with sugar.
Bake 20 minutes. Reduce oven temperature to 350ºF. Bake another 20 to 25 minutes or until fruit juices are bubbling out of vents in piecrust. Let cool on wire rack before serving.