Dissolve the sugar in a heavy bottomed pan until it is completely dissolved and turns brown, forming a caramel.
Remove from the heat and very carefully add a knob of butter.
Whisk in the double cream. Once all the bubbles have gone, add the chopped ginger and syrup. Return to the heat to dissolve any remaining caramelised sugar, stirring occasionally.
Cool slightly before serving over a bowl of vanilla ice cream.