Combine the flour, sugar, and salt in a large mixing bowl.

Cut in the cold butter with a pastry blender or your fingers until the mixture resembles coarse crumbs.

Gradually add ice water, mixing until the dough comes together.

Divide the dough in half, form into disks, wrap in plastic, and chill for at least 1 hour.

In a bowl, mix strawberries and rhubarb with sugar, cornstarch, cinnamon, salt, vanilla, and lemon juice, tossing gently to coat.

Preheat your oven to 400°F (200°C).

Roll out one disk of dough on a floured surface to fit a 9-inch pie pan, then line the pan with it.

Fill it evenly with the prepared fruit mixture.

Roll out the second disk and cut it into 3/4-inch wide strips, place half the strips horizontally across the pie, then weave the remaining strips vertically to create a lattice design.

Trim and crimp the edges of the dough.

Combine the egg and milk, brush over the lattice top, and add coarse sugar on top.

Place the pie onto a baking sheet and bake at 400°F for 20 minutes.

Lower the oven temperature to 350°F and bake for an additional 35–40 minutes or until the crust is golden and filling is bubbly.

Allow the pie to cool completely for at least 2 hours before slicing.