In a large bowl, mix 2 1/2 cups flour and 1 teaspoon of salt. Add the cold butter cubes and toss to coat.
Using a pastry blender or fork, cut the butter into the flour mixture until it resembles coarse sand with some pea-sized pieces.
Gradually add ice water, one tablespoon at a time, tossing with a fork until the dough just begins to clump together. Do not overwork the dough.
Divide the dough into two equal portions. Flatten each into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes.
Preheat oven to 400°F (200°C). Roll out one dough disk into a 12-inch circle to use as the bottom crust of the pie.
In a large bowl, toss the rhubarb and frozen strawberries with 1 cup of the sugar until evenly coated.
Pour the rhubarb-strawberry mixture into the crust and sprinkle with 2 tablespoons of sugar.
Roll out the second dough disk and place it over the filling. Seal and flute the edges. Cut a few slits in the top to allow steam to escape.
Place the pie on a baking sheet and bake for 20 minutes at 400°F, then reduce heat to 375°F (190°C) and bake for 30-35 minutes, or until the crust is golden and the filling is bubbly.
Let the pie cool completely before serving.