Preheat the oven to 180 Celcius.
Melt the butter
Mix the dry ingredients
Make a well in the dry ingredients, pour in the melted butter and mix in.
Press into a small rectangle tin.
Bake for 20 mins. Allow to cool before icing.
Melt the butter and mix in the juice. Pour slowing into the icing sugar and mix it in. Add more butter and juice until you have a nice spreadable consistency.
Ice the slice. Allow the icing to set before cutting and storing in an airtight container.