Prepare the Thai tea according to the package instructions. You will need about 1/4 cup brewed Thai tea.
In a shallow bowl or plate, crack the eggs. Add the milk, Thai tea, and vanilla extract, then whisk until well combined.
Dip each slice of brioche into the mixture for a few seconds, making sure both sides are evenly coated.
Heat a pan over low-medium heat and add butter. Place the soaked brioche slices in the pan and cook until golden brown. Flip and cook the other side until golden and cooked through.
Repeat until all the bread slices are cooked.
Drizzle with condensed milk and enjoy.