Lightly toast the cardamom pods, cloves, peppercorns, and cinnamon stick in a dry skillet over medium heat for 1–2 minutes until fragrant. Remove from heat and bruise the cardamom pods and crush the spices slightly with a mortar and pestle or the flat side of a knife.

Simmer spices and ginger

In a small saucepan, combine 2 cups water, bruised/crushed spices, and sliced fresh ginger. Bring to a gentle boil over medium-high heat, then reduce heat to low and simmer uncovered for 5 minutes to extract the spice flavors.

Add tea and simmer

Add 3 tablespoons black tea leaves to the simmering spiced water. Continue to simmer on low for 3 minutes more, stirring once to ensure tea releases color and flavor but avoiding over-extraction which can make it bitter.

Add milk and sweetener

Stir in 1 cup whole milk and 2 tablespoons sugar (adjust to taste). Raise heat until the mixture is just below a gentle boil (small bubbles at the edge), then reduce heat and simmer for 1–2 minutes so flavors marry. If using vanilla, stir it in now.

Strain concentrate

Remove the saucepan from heat. Strain the chai concentrate through a fine-mesh sieve or cheesecloth into a heatproof measuring cup or bowl to remove solids. Press gently on solids to extract liquid but avoid forcing bitter tannins out.

Cool quickly

Allow the concentrate to cool at room temperature for 10–15 minutes, then transfer to the refrigerator or an ice bath to chill for at least 20 minutes. You should have about 2 cups of chilled concentrate.

Assembly

Fill a 16-ounce (about 2 cups) serving glass with 1.5 cups ice cubes.

Pour 10 ounces (about 1 1/4 cups) of the chilled masala chai concentrate over the ice. Add 2 ounces cold water or cold milk to taste to reach 16 oz total and to adjust strength/creamer mouthfeel.

Stir gently to combine and chill. Taste and add additional sweetener if desired (a quick pinch of sugar stirred into the cold drink or simple syrup works best).

Garnish with a lemon slice or mint sprig if desired and serve immediately.