I used to bake sugar cookies with added stem ginger, but I like them stronger, so I started to experiment. These are much sharper; they may be improved further in the future.
If you want vegan cookies, you can of course use margarine or hard vegetable cooking fat. Oil would probably spoil them.
Sift the flour with ground ginger, cinnamon and salt. Rub the butter into the flour. Add sugar, stem ginger and root ginger to the flour mixture and knead until well mixed. Add a few drops of water if needed to make it hang together.
Make a roll of the dough. Roll it in a mixture of sugar and ginger, then wrap in cling film and refrigerate for at least half an hour.
Preheat the oven to 200°C (390°F).
Cut the dough into slices about 1/2 cm thick and put on a baking tray (they won't expand much). Bake about 15 minutes (about 12 minutes with convection) until just golden and still fairly soft. Put on a rack to cool and harden.