Roll out half of the pastry and place in a 9-inch pie plate. Chill the bottom crust while you roll out the top crust.
1 homemade pie crust for a 9-inch double-crust pie
After rolling the pastry for the top crust, remove bottom crust from the refrigerator. Sprinkle 1/3 of the flour-sugar mixture over the bottom crust. Add half of the rhubarb, followed by half of the raspberries. Sprinkle on half of the remaining sugar mixture. Repeat these layers, ending with the last of the sugar mixture.
3 cups chopped rhubarb, 1 ½ cups fresh raspberries
Top with the pastry for the top crust. Trim and crimp/flute the edges. Use a sharp paring knife to cut slits in the top crust to allow steam to escape.
Set pie on a baking sheet. Bake on the lowest rack for 15 minutes. Reduce oven temperature to 350°F and bake for an additional 40-45 minutes or until crust is golden and the juices are bubbly.
Notes
If you are making this pie with frozen rhubarb and/or frozen raspberries, do not thaw the fruit first. Add it to the pie while it is still frozen.
Check the pie after about 30 minutes to make sure the edges of the crust are not browning too quickly. If you find that they are, you can cover them lightly with foil or a pie crust shield.