In a mixing bowl, whisk together all-purpose flour and salt until well combined. Cut in very cold, unsalted butter until the mixture resembles coarse crumbs. Gradually add ice water, one tablespoon at a time, mixing until a dough forms. Shape the dough into a disc, wrap in plastic, and chill for at least 30 minutes.

While the crust chills, prepare the filling by gently combining fresh strawberries, chopped rhubarb, granulated sugar, cornstarch, lemon juice, and vanilla extract in a large bowl. Stir until the fruit is evenly coated and let sit for about 15 minutes.

Remove one disc from the refrigerator and roll it out on a floured surface to a 12-inch circle. Transfer to a 9-inch pie plate, pressing it gently. Pour the filling into the crust, spreading evenly.

Roll out the second dough disc to a similar size. To make a lattice top, slice the dough into strips and weave them over the filling. Crimp the edges to secure the design. Brush the top with an egg wash.

Preheat your oven to 400°F (200°C). Place the pie on a baking sheet to catch drips and bake for 20 minutes. Reduce temperature to 375°F (190°C) and bake for an additional 35-40 minutes until the filling bubbles and the crust is golden brown.

Allow the pie to cool on a wire rack for at least 3-4 hours before serving to let the filling set.