1. Add all of the gluten free flours to a large bowl. Mix well, weigh out what you need for this recipe, then transfer the rest to a large container with a tight-fidding lid.
2. Preheat oven to 350 degrees F. Lightly butter a 9 x 13 inch baking pan.
3. Whisk the 9 ounces of flour with the baking soda, ginger, cinnamon, and nutmeg. Set aside.
4. In the bowl of a stand mixer, cream the butter with the sugar. Add the molasses and the honey and beat well to combine. Add the eggs one at a time, beating well after each addition.
5. Add the dry ingredients and mix on low speed until just blended. Scrape down any batter on the sides of the bowl, then transfer batter to prepared pan, smoothing it out evenly.
6. Bake for 23-28 minutes, until the bars are uniformly browned and edges are beginning to pull from the sides of the pan. A toothpick inserted in the center should not be completely dry. Note that if you open the oven door toward the end of cooking and see that the bars look puffy, don't worry. The puffiness will subside shortly after. Allow the bars to cool before dusting with confectioner's sugar, or glaze them with the ginger icing.
7. To make the icing, combine the butter with the golden syrup and ginger in a small saucepan. Cook over low heat until the butter melts. Remove from the heat and whisk in the confectioner's sugar. Pour icing over the cooked and cooled bars, spreading it out with an offset spatula. Place in refrigerator for an hour or so until the icing is set, then slice into bars.