Begin with the crust by following my pie crust recipe up until step 5.

To make the filling, combine the sliced rhubarb, chopped strawberries, both sugars, cornstarch, and salt in a large mixing bowl. Add the orange juice and vanilla extract and stir until well mixed. Let this mixture stand while you preheat the oven.

Preheat your oven to 400°F (204°C).

On a lightly floured surface, roll out one disk of chilled dough into a 12-inch circle. Place the rolled dough into a 9-inch pie dish, making sure it sits smoothly against the dish. Spoon the prepared filling into the crust, being careful to leave any excess liquid in the bowl.

Dot the filling with small pieces of butter.

Take out the second disk of dough from the refrigerator and roll it into a 12-inch circle. Cut the dough into 1/2 – 1 inch wide strips using a pastry wheel, sharp knife, or pizza cutter. Weave the strips over and under each other across the pie to form a lattice top. Seal the edges by pressing the strips into the base crust and trim any excess dough. For an alternative topping, cover the filling with a 12-inch dough circle and make slits for steam to escape, or add a crumble topping.

Brush the lattice with the egg and milk mixture, and if using, sprinkle with coarse sugar.

Place the pie on a large baking sheet and bake in the preheated oven for 20 minutes. Without opening the oven, reduce the temperature to 350°F (177°C) and continue to bake for another 30-35 minutes. To prevent over-browning, place a pie crust shield over the pie after the first 20 minutes.

Allow the pie to cool at room temperature for three hours to ensure the filling thickens.

Store any leftovers in the refrigerator, covered tightly, for up to five days.