Fold the custard, clotted cream and ginger syrup together in a bowl until completely combined. Pour this into an ice-cream machine and churn according to machine instructions. (If you don't have an ice-cream machine, put the bowl in the freezer for about 11⁄2 hrs, or until the mixture starts to freeze around the edges. Give it a good stir to break it all up, then repeat.)
When the ice cream is completely churned, mix in the chopped ginger so it speckles the ice cream, then serve in scoops with the Roasted rhubarb.