4 cm piece fresh ginger, unpeeled, coarsely grated
1 cinnamon stick, lightly crushed with the flat side of a knife
6 teaspoons loose strong black tea or 6 tea bags
14 green cardamom pods, lightly crushed, or ¾ teaspoon cardamom seeds, lightly crushed
2¾ cups milk
¼ cup pure maple syrup
Bring ginger, cinnamon, and 3½ cups water to a boil in a medium saucepan over medium-high heat. Lower heat and simmer rapidly, stirring occasionally, until liquid is reduced by a third and very fragrant, about 20 minutes.
Remove pan from heat, stir in tea and cardamom, and let steep 2 minutes.
Return pan to medium-high heat and stir in milk and maple syrup. Cook, stirring occasionally and keeping a close watch, until mixture begins to foam up and boil, about 5 minutes. Immediately remove from heat and let sit 5 minutes. Strain chai through a fine-mesh sieve into a teapot or pitcher and serve.