Place the crust on a lightly floured surface. Roll the dough out into a 12 inch circle.
Once your circle is rolled out, fold the dough in half and pick it up and place into a 9 inch pie plate. Unfold the dough and gently push the dough into the bottom and sides, working out all of the folds.
In a bowl, add in the cornstarch and sugar. Stir until incorporated.
Add in the sliced strawberries and rhubarb and stir until completely coated in sugar and cornstarch.
Pour into the bottom pie crust and spread out.
Roll out the top pie crust on a lightly floured surface to be about 10 to 11 inches.
In a small bowl, add in the egg and water. Beat with a fork or whisk until combined. Using a pastry brush, brush the egg wash onto the bottom edge of the pie crust.
Fold the top layer of pie crust in half and lay it on top, lining it up so the crust crease is in the center. Unfold and gently press the top and bottom dough together around the edges. Cut off the excess dough using a paring knife, leaving about ½ inch overhang.
Fold the ½ inch of overhang dough underneath the bottom crust so the edges are all round and tiny.
Cut a few slits in the top of the crust for the steam to escape.
With your forefinger and thumb, crimp the pie crust together. I form a "U" with my forefinger and thumb on the inside of the edge. With my other forefinger, I push the dough between my thumb and forefinger resting on the inside.
With the pastry brush, brush the top layer with the egg wash.
Place the pie in the preheated 400 degree F oven for 20 minutes and then turn the heat down to 350 and bake another 40 to 50 minutes until the pie filling is bubbling and the crust is golden brown.
If you’re using frozen strawberries or rhubarb, allow the rhubarb to thaw, drain it, and add an additional 2 tablespoons of cornstarch to the recipe.