Preheat the oven to 400°F. Gather and prepare all ingredients.

In a large bowl, combine the rhubarb, strawberries, sugar, cinnamon, cornstarch, lemon juice, zest, vanilla, and salt. Gently fold together and set aside.

Roll out one pie crust, larger than the 9-inch pie pan, and place it on the bottom of the pie pan, pressing the bottom and sides. You want the excess pie crust to be hanging over.

Pour the filling onto the pie crust and evenly top with butter pieces.

Roll out the second pie crust and place on top, pinching the edges with the bottom crust to seal. Crimp the pie crust into decorative edges.

Cut slits in the top pie crust to vent during the baking process. Brush with milk.

With 3-inch strips of tin foil, line the edges of the pie to prevent burning.

Place the pie on an oven-safe tray and place it in the oven. Bake for 30-45 minutes. Remove the tin foil and cook an additional 25-30 minutes until the crust is golden. Remove the pie from the oven and let it cool before cutting.