Boil water.If using an electric kettle with temperature setting, set it at 190°F. If boiling water on the stovetop, let it come to a simmer and turn off heat.
Put Thai tea mix, black tea, and hot water in a teapot and steep for 5 minutes.
Strain out tea leaves and stir in brown sugar.
MAKE WHIPPED CREAM TOPPING
Whip together heavy cream and sweetened condensed milk.Combine heavy cream and 1 tablespoon of sweetened condensed milk in a tall container and whip until it doubles in volume using a handheld milk frother. Set aside.
Blend Thai tea ingredients with ice.Ice, brewed and chilled Thai tea, sweetened condensed milk, and evaporated milk all go into the blender. Blend until smooth. Use a blender tamper tool to get the drink as smooth as possible.
Pour frozen Thai tea into two cups.
Top with whipped cream.Serve with a straw and drink immediately.