01 -  Mix the flour, sugar, salt, cinnamon, and nutmeg in a microwave-safe mug. 
 02 -  Stir in the melted butter, milk, and dark rum (if using) until smooth. 
 03 -  Microwave for approximately 90 seconds or until the cake is set. Ensure not to overcook. 
 04 -  Dust with additional cinnamon and serve immediately while warm.