1. Combine 1 cup sugar with cornstarch; set aside.
2. Heat oven to 375 degrees.
3. Fit one of the pie crusts into a 9-inch pie plate.
4. Set aside.
5. In large bowl, toss rhubarb, strawberries, sugar-cornstarch mixture and lemon juice.
6. Let stand 5 minutes.
7. Pour strawberry mixture into crust-lined pie dish, leveling slightly.
8. Using a knife or pizza cutter, cut remaining crust into 1-inch strips.
9. Interweave into a lattice pattern.
10. Crimp strip edges with bottom crust to seal.
11. Brush crust with milk, then sprinkle with sugar.
12. Bake at 375 degrees for 50 minutes, covering edge of pie with foil if browning too quickly.
13. Cool to room temperature.
14. Serve slightly warm with ice cream, if desired.