Preheat oven to 190 degrees C. Grease one 20x30cm glass baking dish.
Cream 1/2 cup of the butter or margarine with 1/2 cup of the white sugar until light, beat in the egg. Add the baking powder and the salt. Stir in the 2 cups of flour one cup at a time alternating with the yoghurt. Spread batter into the prepared pan. Arrange fruit over top of batter. Sprinkle topping over fruit.
To Make Topping: Mix together 1/2 cup white sugar, 1/2 cup flour, 125g butter or margarine and the cinnamon until the mixture resembles coarse crumbs.
Bake for 1 hour and 15 minutes or until the cake top is puffed and nicely browned. Allow cake to cool. You can serve it directly from the baking dish or for a more attractive presentation, cut it up into squares and arrange them on a platter.