Preheat oven to 190 degrees C. Grease and flour a 23cm round cake tin.
Sift together the flour, baking powder and salt then set aside.
In a large bowl cream together the butter and sugar until light and fluffy. Beat in the egg then stir in the vanilla and milk. Beat in the flour mixture just until incorporated. Pour batter into prepared cake tin.
Bake in the preheated oven for 20 to 25 minutes or until a toothpick inserted into the centre of the cake comes out clean.
Topping: While cake is still warm spread with butter and sift icing sugar and cinnamon over the top.