Prepare Papa's Pie Crust recipe, divide in two, set aside.
In a large bowl, combine strawberries, rhubarb, sugar, cornstarch, lemon juice and cinnamon, gently toss, set aside.
On lightly floured surface, roll out half of the dough and line a 9-inch glass pie plate. Spoon in filling. Cover with top crust, cut away excess dough, seal and flute edges. Make several small slits in the top to allow steam to escape or make a lattice top by rolling out dough for top crust; using pastry wheel or knife, cut into eight 1-inch wide strips. Brush pastry rim with some of the beaten egg. Gently weave strips over the pie to form lattice; trim and flute the edge. Brush top crust with beaten egg. Sprinkle top with 1 tablespoon sugar.
Bake on a baking sheet with sides in a 425 degree oven for 15 minutes. Reduce heat to 375 degrees and bake for 45 to 50 minutes or until rhubarb is tender, and the crust is golden. NOTE: If the edges of the crust start to get too brown, cover with aluminum foil. Transfer pie to wire rack and let cool completely before cutting.