Preheat oven to 400F. Wash, hull, and cut your strawberries into small pieces, then place them in a large bowl. Wash the rhubarb and cut into pieces a bit less than 1/2 an inch, then transfer to the bowl of strawberries.
Sprinkle the sugar, cornstarch, and salt over the mixture, then mix to combine and set aside.
Roll your first piece of chilled pie dough out on a lightly floured surface into a 12 inch round. Keep the dough moving and re-flour as needed.
Transfer dough into your pie dish and push from the outside so it conforms to your pie dish.
Roll the second piece of pie dough out and cut it into roughly one inch thick strips.
Give your filling one last toss then spoon into the pie dish. Excess liquid at the bottom of the bowl is not needed and can be discarded. Smooth the top into an even layer then dot with butter. In a small bowl mix the egg yolk with two teaspoons of water, milk, or cream. Brush the edge of the pie crust then arrange the strips in a lattice on top. Brush the lattice with the egg wash and sprinkle with coarse or granulated sugar if desired.
Bake at 425F for 20 minutes then reduce oven temp to 375F and bake an additional 35-40 minutes. Tent the pie around the 40 minute mark. Allow pie to cool before cutting. Serve with vanilla ice cream.