Preheat oven to 190°C bake. Grease an 18cm x 28cm slice tin and line with baking paper.
Cream butter and sugar until light and fluffy. Sift flour, baking powder and ginger into creamed mixture and mix well (dough will be quite crumbly).
Press dough into prepared tin. Bake for 20-25 minutes, or until light brown.
Pour ginger icing over base while hot. Allow to cool a little, then slice into squares while still warm.
In a small saucepan on medium-low, combine butter, icing sugar, golden syrup and ginger. Heat until butter is melted and mixture is smooth, stirring constantly.