Step 1: Prepare the pie crust by pulsing flour, salt, and 1 tablespoon sugar in a food processor. Add cold butter and pulse until it resembles coarse crumbs. Gradually add ice water until the dough just comes together. Divide into two discs, wrap in plastic, and chill for at least 1 hour.
Step 2: Pre-heat your oven to 400°F (200°C). Roll out one disc of dough on a floured surface and fit it into a 9-inch pie plate.
Step 3: In a large mixing bowl, combine the rhubarb, strawberries, 1 cup sugar, cornstarch, lemon juice, and vanilla extract. Toss gently to coat and let sit for 15 minutes.
Step 4: Pour the fruit filling into the prepared bottom crust. Roll out the second disc of dough and place it over the filling. You can do a solid top with vents or a lattice design.
Step 5: Trim and crimp the edges to seal. Brush the top with a beaten egg wash and sprinkle with coarse sugar.
Step 6: Bake at 400°F for 20 minutes, then reduce the temperature to 375°F and bake for an additional 35-40 minutes until the crust is golden brown and the filling is bubbling thick.
Step 7: Allow the pie to cool completely for at least 4 hours before slicing. This is crucial for the strawberry rhubarb pie recipe filling to set properly.