Preheat your oven to 375°F (190°C).
In a large mixing bowl, combine the sliced strawberries, diced rhubarb, sugar, cornstarch, vanilla extract, and ground cinnamon. Gently toss the mixture until the fruit is evenly coated.
Roll out one pie crust and gently press it into your pie dish, ensuring it covers the bottom and sides.
Pour the strawberry-rhubarb filling into the pie crust, spreading it out evenly.
Roll out the second pie crust and place it over the filling. You can create a lattice pattern or simply cover the pie and cut a few slits to allow steam to escape.
Trim any excess crust hanging over the edges and crimp the edges to seal the pie.
Brush the top crust with the beaten egg, which will give the pie a beautiful golden color while baking.
Place the pie on a baking sheet to catch any potential drips, and bake in the preheated oven for 45-50 minutes, or until the crust is golden brown and the filling is bubbling.
Once baked, remove the pie from the oven and allow it to cool on a wire rack before slicing and serving.