1. Preheat your oven to 375°F (190°C).
2. In a mixing bowl, combine flour and butter until the mixture resembles coarse crumbs. Gradually add ice water until the dough comes together.
3. Divide the dough in half, shape into discs, and refrigerate for at least 30 minutes.
4. Roll out one disc of dough and fit it into a pie dish. Trim the excess dough.
5. In another bowl, mix rhubarb, strawberries, sugar, cornstarch, lemon juice, and vanilla extract. Pour the filling into the pie crust.
6. Roll out the second disc of dough and place it over the filling. Trim, seal, and crimp the edges. Cut a few slits in the top crust to allow steam to escape.
7. Bake for 60 minutes or until the crust is golden and the filling is bubbly. Let it cool before serving.