Add water, cinnamon stick, crushed cardamom pods, cloves, ginger, and peppercorns to a medium saucepan and bring to a gentle simmer over medium heat.
Let the spices simmer for about 8–10 minutes until the liquid becomes fragrant and slightly darker in color.
Add the black tea bags to the saucepan and simmer for another 3–5 minutes, allowing the tea to steep fully.
Stir in the brown sugar until completely dissolved while the mixture is still hot.
Remove the saucepan from heat and stir in vanilla extract if using.
Strain the concentrate through a fine mesh strainer into a heat-safe jar or container, removing all spices and tea bags.
Allow the chai concentrate to cool slightly before storing in the refrigerator for up to one week.
To serve, mix equal parts chai concentrate and milk, then heat or pour over ice for an iced chai latte.
