Coarsely grind orange in processor. Transfer to medium saucepan. Add blueberries, cranberries, sugar, and cornstarch. Stirring constantly, boil mixture over medium high heat until thick, about 3 minutes. Cool completely.
Position the rack in center of oven and preheat to 400 degrees F.
Place rolled piecrust dough in a 9-inch pie plate; press into place. Trim edges to leave 1/4-inch overhang; reserve trimmings. Spoon the berry filling into crust, mounding in center. Dot filling with butter. Roll the second pie crust out on lightly floured surface. Transfer to top of pie; trim edges and pinch edges together to make a seal. Crimp edges for decorative border. Make several slashes in top crust to allow steam to escape. Brush crust with milk.
Gather the reserved crust trimmings and roll out 1/8-inch thick round. Using knife cut out 6 or 7 small leaf shapes. Place leaves decoratively atop pie. Press gently. Brush leaves with milk. Sprinkle pie with sugar. Place on rimmed cookie sheet and bake until crust is golden brown, about 50 minutes. Cool on rack for 1 hour. Serve.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.