Preheat the oven to 360 F (180 C). Line a 12 hole muffin tin with patty cases. In a large mixing bowl, sift the flour, cocoa powders, baking soda, baking powder and then add the sugars – give it a stir. Pop the butter into the microwave for a short burst, 10 seconds or so at a time, until it is JUST melted. Give it a stir with a fork to eliminate any lumps. In a separate mixing bowl, add the eggs, vanilla and butter and whisk together until smooth. Then add the wet mixture into the dry mixture, along with the buttermilk and gently fold until just combined.