In a blender, blitz the dark brown sugar, granulated sugar and Thai tea until it becomes a fine powder
Add the blitzed sugar and Thai tea mixture to the egg yolks and place over a double boiler, whisking until doubled in size
Add the vanilla and salt and set aside
In another bowl, add the mascarpone and heavy cream, whipping until medium peaks form about 5 minutes
Add the egg yolk mixture to the cream and gently fold until incorporated
Steep the Thai tea with 1 ½ cup hot water and let it sit for 5 minutes, then strain well
Dip each ladyfinger into the Thai tea soak and cover the bottom layer of the baking dish
Add ½ of the cream mixture and evenly spread over using a spatula
Repeat the ladyfinger and cream layers once more
Chill for at least 5 hours, ideally overnight
Before serving, dust with finely powdered Thai tea or cocoa powder
