Preheat the oven to 350°F and generously grease a 9-cup muffin tin with unsalted butter.

Warm the full can of coconut milk in a saucepan over medium heat until it gently begins to boil.

Steep the Thai tea leaves in the heated coconut milk, then remove from heat and cover for 7 minutes.

Mix the dry ingredients in a separate bowl: Mochiko rice flour, dark brown sugar, baking powder, and salt.

Strain the steeped tea leaves from the coconut milk. Add the egg, vanilla, and melted butter to the coconut milk and whisk until well combined.

Combine the wet and dry mixtures by gradually stirring the dry mixture into the wet ingredients until fully integrated.

Pour the batter into the muffin tin, filling each cup about a quarter inch from the top.

Sprinkle black and white sesame seeds on top of each muffin.

Bake the muffins for 55-65 minutes, or until a toothpick inserted comes out clean.

Cool them in the pan for a couple of minutes before transferring to a wire rack.