Make the pastry: Sift the flour, sugar, and salt together. Stir in the butter, lemon juice, and eggs. Turn out onto a lightly floured surface and briefly knead. Shape into a ball and cover with a damp cloth. Chill for 1 hour. Bring a pot of water to a boil. Blanch the swiss chard, and cook for 10 minutes, add the spinach and continue to cook for 5 more minutes. Run under cold water and drain. Squeeze out excess water and finely chop. Preheat oven to 375 degrees. In a small sauce pan cook the sultanas or raisins in the rum until almost all the rum is absorbed, about 2 minutes. Cool then mix with the swiss chard, spinach, pine nuts, sugar, 2 eggs, and lemon zest. Lightly butter a 12-inch by 10-inch baking dish. Divide the dough into a one third piece and a two third piece. On a lightly floured surface, roll the two thirds portion of dough into 1/8-inch thick rectangle. Line the bottom and sides of the baking dish. Prick all over with a fork and add the swiss chard mixture. Arrange the apples in a single layer over the chard. Roll out the remaining dough to 1/8-inch thick rectangle. Cover the filled baking dish with the dough. Crimp edges, trim excess and prick with a fork. Brush the top with the beaten egg yolk. Bake for 30 minutes or until the dough is crisp and golden.