1. Heat oven to 425 degrees. On a lightly floured surface, roll out one disk of dough into a 12-inch circle, about 1/8 inch thick. Transfer dough to a 9-inch pie plate, gently pressing dough into pan. Trim dough 1/2 inch larger than pan; tuck excess under, forming a thick, rolled crust. Chill.

2. In a large bowl, combine plums, sugar, flour, and cornstarch; toss to combine. Add raspberries, and gently toss to combine. Transfer mixture to chilled crust. Dot with butter, and return to refrigerator.

3. Roll out remaining disk of dough into a 10-by-12-inch rectangle, about 1/8 inch thick. Using a fluted pastry wheel, cut dough into twelve 3/4-inch-wide strips. Lightly brush lower third of each strip with water. Place strips on top of fruit, and weave a lattice. Trim edges flush with pie pan, and gently press to seal. Chill pie 20 minutes more.

4. Place pie on baking sheet; bake until crust begins to turn brown, about 20 minutes. Reduce heat to 375 degrees, and bake until crust is brown and fruit is bubbling, 40 to 50 minutes. Transfer to a wire rack to cool. Serve.