Perfect Rhubarb Pie
["4 c. sliced fresh rhubarb", "4 c. boiling water", "1 1/2 c. sugar", "3 Tbsp. all-purpose flour", "1 tsp. quick cooking tapioca", "1 egg", "2 tsp. cold water", "pastry for double crust pie (9-inch)", "1 Tbsp. butter or margarine"]
["Place rhubarb in a colander and pour water over it; set aside.", "In a bowl, combine sugar, flour and tapioca; mix well. Drain rhubarb; add to sugar mixture and toss to coat.", "Let stand for 15 minutes.", "Beat egg and water; add to rhubarb mixture and mix well.", "Line a 9-inch pie plate with bottom pastry.", "Add filling.", "Dot with butter.", "Cover with remaining pastry; flute edges.", "Cut slits in top crust.", "Bake at 400\u00b0 for 15 minutes. Reduce heat to 350\u00b0 and bake 40 to 50 minutes longer or until crust is golden brown and filling is bubbly."]
["fresh rhubarb", "boiling water", "sugar", "flour", "tapioca", "egg", "cold water", "pastry", "butter"]