In a large bowl, cream together 65g butter and 1/3 cup of sugar until smooth. Beat in egg and vanilla until well blended. Combine 1 1/2 cups of flour, salt and baking powder; stir into the creamed mixture alternately with the milk. Spread evenly in a 20cm x 20cm baking pan.
In a small bowl, stir together 2 tablespoons flour, 5 tablespoons sugar and cinnamon. Add 2 tablespoons of butter and pinch into the dry mixture using your fingers until the mixture is crumbly. Sprinkle over the top of the cake.
Bake for 25 minutes in the preheated oven, until a knife inserted into the centre comes out clean.