I’ve generally had good luck finding this at Asian grocers… It can be used as the base for the kind of Thai tea you get from a restaurant, just add sweetened condensed milk. I’m not a huge sugar fan so I drink it straight. Even then, it has a nicely bold flavor, and an incredibly high caffeine content.
It’s always worth experimenting. I will say, this tea has a pretty peculiar flavor that, even when you taste it black, you can strangely sense that it would go well with sweetened milk.