Make the Pie Dough (makes 3 single 9 inch pie shells)
1. In the bowl of a food processor, add 2 1/4 cups flour, 1/4 cup granulated sugar and the salt. Pulse to combine. Add in 8oz butter and pulse until it looks like coarse crumbs.
2. Add in the water and pulse just until the dry ingredients are incorporated and the dough forms a ball. Divide into 3 equal parts and wrap individually in plastic wrap. Refrigerate for 1 hour, overnight or freeze for up to 2 months.
Make the Crumb Topping
1. In the same food processor bowl add the remaining 2 cups of flour, 1/2 cup granulated sugar, 1/2 cup brown sugar and the remaining 8oz butter. Pulse until combined.
2. Reserve 2 cups for the pie. Freeze the rest for another use.
Make the Filling
1. In a large bowl add the rhubarb, strawberries, the remaining 1/2 cup granulated sugar, orange zest and cornstarch. Mix well.
Assemble the Pie
Preheat oven 375° F. Set the oven rack to bottom third position,
1. Roll 1 piece of the pie dough into 14" round on a well floured surface. Roll from the center to the edge, turning and flouring the dough to make sure it doesn't stick to the board.
2. Fold the dough in half, place in a pie pan, and unfold to fit the pan. Using kitchen shears or a sharp knife, trim the dough to an even 1-inch overhang.
3. Tuck the overhang under itself to create a rim; press to seal. Crimp the rim with your thumb and forefinger, or press with the tines of a fork.
4. Add the filling, and top with crumb topping. Place the ready to bake pie on a rimmed baking sheet to catch any drips.
5. Bake for 40 minutes.