Quick Apple Tarts

In large bowl with electric mixer, beat together butter and sugar until light and fluffy; beat in egg and salt. Gradually stir in flour until soft dough forms. Heat oven to 375 °F (190°C) . On lightly floured surface, roll dough into a 10-inch square; cut into four 5-inch squares. Place squares on baking sheet; turn up 1/4 inch of edges of all squares to make a thick edge. Arrange apples slices on each square; sprinkle each with 1 teaspoon sugar. Bake 20 to 25 minutes or until pastry is golden. Brush apple slices with marmalade and return to oven for 3 minutes.