1. Combine flour, butter and salt in a food processor. Pulse until butter is the size of peas. Slowly stream in 1/4 to 1/2 cup ice water, until dough just comes together (squeeze between your hands). Form into 2 equal rounds, wrap in plastic wrap and refrigerate 2 hours.
2. Heat oven to 375 degrees . On a lightly floured surface, roll one round of dough to fit inside a 9-inch pie dish. Refrigerate 15 minutes.
3. Combine grapes, granulated sugar, tapioca and lemon juice. Transfer to pie crust. Roll out second crust and cut out about 18 three-quarter-inch circles with a pastry cutter. Place crust on top of pie and pinch edges of both crusts together, then crimp. Brush top and edges with egg, then sprinkle on coarse sugar.
4. Bake pie at 375 degrees for 30 minutes. Carefully wrap foil around edges of crust to prevent burning, then bake another 30 minutes, until golden brown. Allow pie to cool completely on a wire rack before slicing.