3-1/4 cups all-purpose flour
1 teaspoon salt
1 cup butter
3/4 cup plus 1 to 2 tablespoons 2% milk
1 large egg yolk
2 cups sugar
1/3 cup cornstarch
5 cups fresh or frozen unsweetened raspberries, thawed and drained
3 cups sliced fresh or frozen rhubarb, thawed and drained
1-1/4 cups confectioners' sugar
1/2 teaspoon vanilla extract
5 to 6 teaspoons 2% milk
In a large bowl, combine flour and salt; cut in butter until crumbly. Whisk 3/4 cup milk and egg yolk; gradually add to flour mixture, tossing with a fork until dough forms a ball. Add additional milk, 1 tablespoon at a time, if necessary.
Divide dough in two portions so that one is slightly larger than the other; wrap each in plastic wrap. Refrigerate 1 hour or until easy to handle.
Preheat oven to 375°. Roll out larger portion of dough between two large sheets of lightly floured waxed paper into an 18x13-in. rectangle. Transfer to an ungreased 15x10x1-in. baking pan. Press onto the bottom and up sides of pan; trim pastry to edges of pan.
In a large bowl, combine sugar and cornstarch. Add raspberries and rhubarb; toss to coat. Spoon into pastry.
Roll out remaining dough; place over filling. Fold bottom pastry over edge of top pastry; seal with a fork. Prick top with a fork.
Bake until golden brown, 45-55 minutes. Cool completely on a wire rack.
For icing, combine confectioners' sugar, vanilla and enough milk to achieve a drizzling consistency; drizzle over pie. Cut pie into squares.