Preheat oven to 400°F. In a large bowl, combine and blend strawberries, rhubarb, sugar, lemon juice, and cornstarch. Pour mixture into pie crust. Place top crust and brush with egg whites and sprinkle with coarse sugar. Place the pie on a baking sheet. Bake for 10 minutes on the oven’s middle rack, then reduce temperature to 350°F. Bake about one hour, until the filling thickens and bubbles.