Mix all dry ingredients (tapioca starch, rice flour, baking powder, salt) in a bowl
In a separate bowl, combine wet ingredients: eggs, coconut milk, pandan extract, and sugar
Incorporate dry ingredients into wet ingredients in batches, being careful not to overmix
Run the batter through a sieve to remove clumps
Preheat oven to 350°F and coat a bun pan with butter
Pour batter into prepared pan
Bake at 350°F for 45 minutes, rotating halfway through
Turn off oven and let cake sit inside with door slightly cracked open for 15 minutes
Remove from pan and cool
