Prepare the pastry dough according to package or recipe instructions. Split into two, set aside.
In a medium sauce pan, bring the rhubarb, strawberries, sugar and juice from a half lemon to a simmer. Add flour to thicken the sauce as needed. Cook for about 8-10 minutes. Let it cool down completely.
Grease a 9 inch pie plate and carefully lay one pastry crust into the plate. Make sure the dough cover the entire surface. Trim the remaining dough of the edge.
Add filling to the pie shell evenly.
Arrange the second half of the pastry dough onto the top of the pie. At this point you can get pretty fancy and create a fun design for or keep it simple and traditional by covering the entire surface. In this case, you will need to "slice" a few cuts open to let the pie breath as it cooks. Brush with milk and sprinkle with sugar (the sugar is optional).
Bake for 40-45 minutes or until golden brown. Serve warm with a scoop of Vanilla Ice Cream.
For this recipe I followed the step-by-step photo tutorial on how to make a lattice pie crust by Ali of Gimme Some Oven!