For golden syrup ice-cream, cook golden syrup in a saucepan over medium heat until dark caramel (4-5 minutes). Remove from heat, add butter and ½ tsp sea salt flakes and swirl to combine, then whisk in cream and return to heat. Add half the milk, whisk to combine and remove from heat. Whisk yolks in a bowl until pale (1-2 minutes), then add milk mixture in a thin steady stream, whisking continuously until incorporated. Return to pan and stir continuously over low heat until thick (3-4 minutes). Transfer to a bowl placed over another bowl of iced water. Add remaining milk, stir occasionally until cool, then refrigerate to chill. Churn in an ice-cream machine, then transfer to a container and freeze until required. Makes about 1.2 litres.
Preheat oven to 160C and line 2 baking trays with baking paper. Combine flour, oats, coconut, sugar and ginger in a bowl. Stir butter and golden syrup in a saucepan over low heat until melted, then remove from heat. Combine bicarbonate of soda with 2 tbsp hot water, stir into butter mixture, then pour into oat mixture and mix well. Roll level tablespoonfuls of dough into balls and place on trays, press lightly and bake in batches until golden (14-16 minutes). Set aside to cool.
To serve, sandwich scoops of golden syrup ice-cream between Anzac biscuits and eat immediately or freeze for later.