In your microwavable mug, mix together the egg, milk, syrup, cinnamon and salt until all combined. (Whisk the egg and milk together before adding other ingredients.)
Butter the bread and slice it into pieces.
Add the bread to the mug and press them down so they are submerged within the liquid and the bread soaks in the egg mixture.
Add the chocolate chips, nuts or fruit to the mug and give a little stir to incorporate it in the mixture.
Sprinkle the optional cinnamon sugar on top.
Microwave for a total of 2 minutes stopping every 30 seconds. (Count to ten and start again - this is so it doesn't explode in your microwave.)
Let cool for about 1-2minutes.
Sprinkle powdered sugar on top. Enjoy!