In a large bowl combine the sugar, tapioca flour, and zest. Add rhubarb and toss to coat.
Sprinkle 1 tablespoon coarse sugar over the bottom of the pie crust, to help keep it from getting soggy. Pour rhubarb mixture into pie pan.
Cut butter into small pieces and dot over the top of the rhubarb filling.
Roll out second pie crust and place on top. Trim, seal and flute edges and cut a few slits (a small X) on top to allow air to escape.
Bake at 400 degrees F for about 1 hour (tent the top of the pie loosely with aluminum foil part way through cooking to keep the crust from browning too much).
Remove from oven and allow to cool for at least 4 hours before cutting. After it cools, refrigerate for up to 4 days.
To Make Ahead: This pie can be made ahead and refrigerated for up to 4 days. The homemade pie crusts can also be made ahead and stored in the fridge or freezer. Follow my instructions HERE.To Freeze: Bake the pie and allow it to cool completely. Cover well with plastic wrap as well as tinfoil. Store in the freezer for up to 3 months. To thaw, place it in the refrigerator for about 1 1/2 days.Strawberry Rhubarb Pie: Substitute 2 1/2 cups of the rhubarb for chopped strawberries! Follow instructions and bake as directed.Rhubarb Crisp.