Heat oven to 350 (180C) and line a 11” x 7” rectangular baking pan with parchment paper.
Take a small saucepan and melt the butter and sugar together over a low heat.
Take the saucepan off the heat and sift in the flour, baking powder and ground ginger. Stir the mixture until well combined.
Spoon the mixture into your prepared pan then press down and spread the mixture evenly taking care to get it in to all the edges of the tin.
Bake for around 15 minutes or until the slice is golden brown. Remove the baking pan from the oven and set aside. You want to make the frosting at this stage, so you can ice the slice while it’s still warm.
For the frosting take a small saucepan and melt the butter and golden syrup/ corn syrup over a low heat. Whisk in the ground ginger and icing sugar, until the frosting is smooth and thick.
Pour the frosting into the center of the slice then lean the pan bake and forward, from side to side until the frosting has covered the slice (take care and hold the pan with a dish cloth if it’s still hot!).
Slice the crystallized ginger, and sprinkle over the frosting along with the pistachio nuts. Allow to cool before slicing.