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 45-55 minutes or until golden brown. 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.
Editor's Note: If using frozen rhubarb, measure rhubarb while still frozen, then thaw completely. Drain in a colander, but do not press liquid out.
Nutritional Facts: 1 piece equals 247 calories, 8 g fat (5 g saturated fat), 29 mg cholesterol, 159 mg sodium, 42 g carbohydrate, 2 g fiber, 3 g protein.