This is the pie for rhubarb lovers. It’s simple, as to best highlight the fresh, seasonal rhubarb, and the shortcut of using a pre-made pie crust helps shave off some time and frustration. All the ingredients are easy to find, especially in the spring, but be sure to use fresh rhubarb—frozen has too much water. Fresh, seasonal rhubarb will have stalks that are between 7 and 15 inches long—length, not color, is the best way to determine ripeness. Processing the tapioca helps incorporate it, and allowing the mixture to stand before transferring it to the pie shell helps it begin to break down. Serve with sweetened whipped cream or vanilla ice cream.