Preheat the oven to 350*F. Butter an 8-inch square baking tin and line with baking paper.  Set aside.

Beat the egg WHITES until stiff and set aside.

Sift the flour, baking powder, and cinnamon into a bowl.  Set aside.  

Cream together the butter and sugar until light and fluffy.  Beat in the egg YOLKS one at a time.   

Beat in the flour mixture along with the milk making alternate additions.  (3 dry and two wet)  

Mix well together.

Fold in the egg whites.  

Spread the batter in the prepared baking tin.  

Bake in the heated oven for 30 to 35 minutes, until the top bounces back when lightly touched and a toothpick inserted in the centre comes out clean.  The cake should also have begun to pull away from the sides a bit.   

Remove from the oven.  Cool in the pan for five minutes then lift out onto a wire rack to finish cooling completely.

Place the butter for the icing in a saucepan and melt over low heat. 

Add the maple sugar and heat gently over low heat for 2 minutes, until the sugar has melted.  Add the milk.  

Bring to the boil, then remove from the stove and let cool.  Beat in the icing sugar and spread onto the cooled cake.