Preheat oven at 180 C or 350F. Line a square (20cm/8inch) baking tin with baking paper.
Place flour, sugar and ginger powder into a mixing bowl and mix with a whisk to combine. Put the cubed butter on top and combine using a pastry cutter or food processor. Stop combining when the mixture has no visible flour and resembles coarse crumbs.
Press the shortbread mixture evenly onto the bottom of the baking tin and bake for 20 minutes. The bottom and top edges should just be starting to brown.
While the base is baking, prepare the icing. Place the butter, golden syrup, icing sugar, ginger powder, and salt into a small saucepan and gently heat it up at a medium heat. When the mixture has come together and is just beginning to boil, you can remove it from the heat. Remember to stir regularly. Let it cool slightly while the base continues to bake.
When the base comes out of the oven, gently pour the hot ginger icing over the base. I poured the ginger icing over a fine strainer so that any stray chunks of sugar and bubbles in the ginger icing can be removed. Let cool before cutting.
When the ginger crunch slice is at room temperature, cut it into even squares. Dip you knife into hot water and wipe off the water before each cut. Store in an airtight container in the fridge for up to a week.
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.