Preheat the oven to 180ºF, 350ºC, Gas mark 4. Line and grease a 23cm round cake tin. Combine the dry ingredients together and place in a mixing bowl. Cream together the margarine and sugar together until light and smooth. Add the yogurt, vanilla essence to this mixture. Mix in the all the dry ingredients followed by the eggs into the cake mixture. Stir in the chopped apples and chocolate drops and pour into the prepared cake tin. Stir the dry streusel ingredients together - the rolled oats, chopped nuts, brown sugar and cinnamon. Whisk the egg white and vegetable oil together. Stir this into the dry streusel ingredients and pour over the top of the cake mixture. Bake in the pre-heated oven for about 1 hour or until the mixture in the centre is cooked. *Some Kosher products may be available in limited stores.
