- Grease the mugs with butter, Break the Dark Fantasy Choco Fills biscuits into chunks and set aside. Mix the flour, baking powder, sugar, egg, milk, vegetable oil, and vanilla extract in a bowl to make a smooth batter. Add the chunks of Dark Fantasy cookies into the batter and mix well. Pour the batter into the mugs and microwave it for 90 seconds. Let the cake cool down for about 10 minutes and Dark Fantasy Mug Cake is ready.