Freeze the ginger whole overnight. This tenderises the ginger and also makes it easier to peel.
Remove the ginger from the freezer and allow to return to room temperature so you can handle it. Peel the ginger and slice into pieces. Feel free to slice first then peel, this can help if you have a particularly knobbly piece of ginger.
In a lidded saucepan place the ginger pieces and 500mL of water. Bring to the boil then reduce to a simmer and cook the ginger pieces for 2.5 hours.
Check the the ginger is tender. If so, drain the ginger but keep the water.
Measure out 200mL of the cooking water and add it to the saupan. Add the sugar, stirring to dissolve.
Once dissolved bring the mixture to a boil, then add the ginger pieces back to the syrup.
Reduce the heat and simmer the ginger pieces in the syrup for 20 minutes.
Remove from the heat and pack into sterilised jars. Place the pieces of the ginger in first, then top up with syrup to cover the ginger. If any syrup is leftover this can also be stored and used as a sweet addition to drinks and tea.
Notes
This recipe is a smaller volume than what I've found elsewhere online. It's great as a small batch to make for yourself to use at home. It filled two little IKEA jars (130mL each) and gave me an extra 100mL of syrup that I've got in the fridge.