1. Make up pastry using the first four ingredients.
2. Place flour in mixer; add fats and mix on low speed until mixture resembles fine breadcrumbs.
3. Add the water and bind together.
4. Roll out pastry and line tray. Crimp edges, prick base and bake blind until pastry is nearly cooked.
5. Cream margarine and sugar until light and fluffy, gradually add in beaten egg.
6. Mix semolina with baking powder and add to mixture. Add water.
7. Spread jam thinly over pastry, sprinkle currants over jam, spread mixture on top.
8. Bake on Gas Mark 4, 180°c, 375°f  for 20-30 minutes.
9. Dust with icing sugar.