Peel the ginger and the lemongrass and roughly chop the peelings. Set aside.
Cut the ginger flesh into fine strips and cook in boiling water for 1 minute. Drain and refresh in cold water. Set aside.
In a saucepan on a high heat, cook the golden syrup for 2 to 3 minutes until it becomes a dark caramel colour. Add the vinegar and simmer until reduced by half. Add the ginger peelings, lemongrass, soy sauce, stock, brandy and cream. Bring to the boil, then simmer uncovered for 10 minutes. Strain the sauce through a fine sieve.
Stir the cooked ginger strips into the sauce and season.