Preheat oven to 180 degrees C. Grease and flour one 18x18cm square baking pan.
Boil sugar, raisins, butter and the water until the raisins absorb most of the water and are quite soggy and mushy. Set aside and let cool completely.
Sift the flour, cinnamon and the baking powder together. Stir the flour mixture into the raisin mixture and mix until just combined. Spread the batter into the prepared pan.
Bake in the preheated oven for 40 to 45 minutes or until cake springs back upon the touch. Immediately put on a wire rack to cool. This is a very soft cake, liable to break easily. Take care when you cut the cake.