The ingredients for Thai tea are water, Thai tea (cha Thai), sugar and evaporated milk. It is usually brewed strong and then blended with a rich swirl of evaporated milk.
Brew strong black (or Thai) tea. If possible, spice tea with orange blossom water, star anise or tamarind. In a glass add tea, sugar, ice and evaporated or condensed milk.
The secret ingredient is condensed milk. You can buy this in small cans at virtually any supermarket. It has a lot of calories, so use it sparingly if you are trying to watch your caloric intake.