On a lightly floured surface, roll out one pie dough disc into an 11-inch circle. Fit the dough into a 9-inch pie pan and refrigerate.
Roll the other disc into a 10-inch circle, place on a large baking sheet, and refrigerate.
Preheat the oven to 400°F. Make the Strawberry-Rhubarb Filling: Whisk together the sugar and cornstarch in a large bowl.
Add the rhubarb, strawberries, vanilla extract, and almond extract and toss to combine.
Spoon the filling into the prepared pie crust. Dot the top of the filling with the butter.
Cut the 10-inch circle into 1-inch-wide strips. Arrange the strips on the filling in a lattice pattern. Fold the edges under and crimp the edges.
Whisk together the egg and 1 teaspoon water. Brush the lattice with the egg mixture. (Avoid the edges of the pie if possible.) Sprinkle with coarse sugar if desired.
Bake the pie for 45 to 50 minutes, until the top is nicely browned and the filling is bubbly. (Shield the edges after 35 minutes if the crust is becoming too browned.) Remove the pie to a wire rack to cool completely.