Preheat oven to 275°C (525°F). Add the tea leaves to room-temperature milk and allow it to seep for 10 minutes. Pour through a sieve, coffee filter or tea screen to strain out the tea. Combine together the flour, baking powder and salt in a large bowl. Set aside.

Using an electric mixer fitted with a paddle attachment on medium speed, cream the butter and sugar until light and fluffy (4–6 minutes). Beat in the eggs 1 at a time, making sure each egg is fully incorporated before adding the next. Alternate incorporating the dry mixture and the Thai tea milk to the batter. Scrape down the sides of the bowl to ensure that the batter is evenly mixed. Scoop the batter into a cupcake pan fitted with paper liners. Bake until a toothpick inserted into the center of a cupcake comes out clean, 18–20 minutes. Cool cupcakes on wire rack.