Step 1

Place 2 cups whole milk, 1/2 cup heavy cream, 1/2 cup granulated sugar, and 1/4 teaspoon kosher salt in a large saucepan (the wider, the better). Bring to a simmer over medium heat, whisking until the sugar is dissolved.

Step 2

Reduce the heat as needed to maintain a brisk simmer. Cook, whisking and scraping down the sides of the saucepan with a flexible spatula every 5 minutes, until reduced to 1 cup, 35 to 60 minutes (a wider saucepan will be faster). The mixture will be thickened to the consistency of gravy and slightly darker (it will not be perfectly smooth). Meanwhile, make the tea.

Step 3

Bring 5 cups water to a boil in a medium saucepan over medium-high heat. Add 12 black tea bags or 1/2 cup loose-leaf black tea. Reduce the heat to medium-low and gently simmer for 5 minutes.

Step 4

Take the saucepan off the heat and let the tea steep for 10 minutes. Pour through a fine-mesh strainer into a medium heatproof bowl. Gently press on the tea leaves or tea bags with a spoon to release as much liquid as possible; discard the tea bags or leaves.

Step 5

When the milk base is ready, transfer it to a blender, making sure to scrape the mixture from the sides of the saucepan into the blender; blend on low speed until smooth. Add the tea and blend again on low speed until smooth. To serve hot, pour back into a clean saucepan and reheat over medium heat if desired. To serve cold, refrigerate until chilled, rewhisk or reblend, and pour over ice.