Divide the pastry almost in half and roll out the larger half, on a lightly floured surface, to a 13-inch circle. Line a 9-inch pie plate with the pastry and trim the pastry 1/2 inch beyond the rim of the pie plate. Combine the raisins, brown sugar, corn starch and drink mix in a 3-quart saucepan.
Stir in the water and lemon juice. Cook over medium heat, stirring constantly, until the mixture boils and thickens.
Remove from the heat and stir in the walnuts.
Turn the mixture into the pastry-lined pie plate and dot with the butter.
Roll out the remaining pastry to an 11-inch circle. Place the top crust over filling and trim the edge to 1-inch beyond the rim.
Fold the top crust under the bottom crust and form a ridge. Flute the edge and cut steam vents in the top crust. Bake in a preheated 400 degree F.
oven for 30 minutes or until the crust is a golden brown and the filling is bubbly.