Pour 2 cups of filtered water into a saucepan and bring it to a rolling boil.

Remove from heat, add 2 tablespoons of black tea leaves or tea bags, and steep for 5 minutes.

Strain the tea using a fine-mesh strainer into a bowl or pitcher.

While warm, whisk in 2 tablespoons of unsweetened cocoa powder and 1/4 cup of sugar until dissolved.

Let the mixture cool to room temperature, then refrigerate for at least 30 minutes.

Fill a tall glass with ice cubes, pour in 1 cup of milk, and then add the chilled cocoa tea mixture. Stir well.

Garnish with chocolate shavings or cocoa powder if desired and serve immediately.