In saucepan combine raisins, 1 1/2 cups water and 1/2 cup sugar and bring to a boil. Combine the remaining 1/2 c water and 1/2 cup sugar, plus flour, egg yolks and salt, add to raisin mixture. Cook until thickened, stirring constantly. Remove from heat and add butter and vinegar or lemon juice.
Pour mixture into baked pie shell. Cover with whipped cream or meringue.