In a large pot over high heat, combine the water and Thai tea leaves. Bring the tea to a boil, then immediately pour the tea through a strainer into a heat-proof vessel to remove the tea leaves. Let the tea cool to room temperature.
Make the simple syrup: in a small pot over high heat, combine the sugar and water. Bring to a boil and cook, stirring occasionally, until the sugar has dissolved and the syrup is clear.
Assemble the tea: divide the ice between 2 glasses, then add simple syrup, tea, and half-and-half.