Preheat oven to 190°C bake. Grease an 18cm x 28cm slice tin and line with baking paper.
Cream butter (125 g), softened and sugar (½ cup) until light and fluffy. Sift flour (1½ cups), baking powder (1 tsp) and ground ginger (1 tsp) 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 (125 g), icing sugar (1¼ cups), golden syrup (3 Tbsp) and ground ginger (4 tsp). Heat until butter is melted and mixture is smooth, stirring constantly.