Peel the ginger using a knife or spoon to remove the skin.
Crush mint in a small bowl using a small mortar and pestle (I used a wooden lemon juicer). Set aside.
Then chop ginger into rough chunks, small enough to blend easily in a blender or food processor. An alternative method would be to use a microplane or fine edge of a grater. (Don't cut ginger in chunks if using a grater to grate the ginger.)
Bring about 7 cups of water to a boil in a kettle or pot.
While water is heating, place ginger into a blender, cover with 1 cup water, and blend until the ginger is thick and pasty.
Add the ginger paste to a large bowl with mint and boiled water.
Strain ginger in cheesecloth over a large bowl or cup, then squeeze the juice from the ginger paste and let it fall into the bowl. Discard the remaining pulp.
Stir lemon juice and sugar into ginger juice until the sugar dissolves, and serve garnished with mint leaves.
Serve with ice if desired. Some people like it hot.