Crush the ginger with a mortar and pestle till it disintegrates into small bits and set aside.
In a medium pot, bring the water to a simmer over medium heat. When you see small bubbles at the bottom of the pot, add the crushed ginger and the tea.
When the water comes to a rolling boil, turn the heat off and cover the pot. Steep the tea for 3 minutes.
Meanwhile, put the condensed milk (or milk powder and sugar) in a small pitcher.
Strain the tea into the pitcher through a fine mesh strainer. Stir until all the ingredients are fully combined.
Aerate the tea by transferring it between the pot and the pitcher a few times or by using an electric frother.
Serve and enjoy!