Prepare crust. Make two sections in processor.
For each section, combine:
4 cups pastry flour
2 cups all purpose flour
2 1/4 tsp. salt
with 4 1/2 cups shortening or butter combination, until it looks like cornmeal
Gradually add 1/2 cup + 2T. ice water until crust holds together.
Shape into two rectangles, and wrap in plastic and refrigerate for half hour.
Roll bottom crust.
Place half of the following mixture over the bottom crust, and toss the other half with 4 lb. (14 cups chopped rhubarb):
1 cup flour
2 1/4 cups white sugar
1/2 cup brown sugar
Place rhubarb with mix on bottom tart crust (which has the other half of the crumb mixture).
Sprinkle 2-3 cups frozen raspberries over rhubarb and add chunks of butter if desired.
Roll crust on top. Pinch pie crust edges. Bake 15 minutes at 425; then 45 minutes at 350.
This tart may run in the oven, so make sure there is foil around the bottom of the pan, overhanging to catch drippings.