I used a Chemex (with a Chemex filter) but you can totally use a measuring cup or bowl and combine the hot water and tea and run it through a strainer.
If you’re using a Chemex, place the filter atop and add the tea to the filter. Pour 2 1/2 cups of hot water over the tea and allow to steep and strain through. Immediately add the tea to a bowl or large measuring cup and stir in 1/3 cup sugar until it has dissolved. You want the tea to be hot/warm so the sugar will dissolve.
In a small saucepan, add half of the coconut milk and heat until it’s very warm. Add the 1/4 cup sugar and mix until dissolved. Transfer the coconut milk to a measuring cup or small bowl and add the remaining coconut milk. Transfer the thai tea and the coconut milk to the fridge until it’s chilled, about 30 minutes to 1 hour.
Fill each mold about 3/4 of the way with the thai tea and top off with the coconut milk.