Preheat the oven to 425° F/220° C. Line the pie pan with the bottom crust, leaving about 1-inch overhang. Keep the top crust refrigerated until ready to cut.
In the large mixing bowl, whisk together the sugar, flour, cinnamon, and salt. Sprinkle vanilla extract over the strawberries, and toss the rhubarb and strawberries in the sugar and flour mixture.
Roll out the top crust and cut into strips ½ to 3/-inch wide. Weave the strips, laying the ends across the overhanging bottom crust. Fold up the bottom crust over the strips and tuck them in, using a drop of water to seal as needed. Crimp the edges.
Place the pie on a baking sheet lined with foil. Bake on the bottom rack of the preheated oven for 15 minutes, then reduce to the temperature to 350° F/175° C. Bake until the filling is bubbly and the pastry golden brown, about 40 to 50 minutes more. Remove from the oven and cool on a wire rack for at least 15 minutes. Serve warm or at room temperature.