Step 1

Very lightly coat the inside of a 6- or 8-ounce mug or ramekin with a smidgeon of cooking spray, butter or coconut oil. Mix all the ingredients together in the mug (to avoid the batter being crumbly, mix the butter, egg yolk, sugars and salt first before gradually stirring in the flour and adding the chocolate chips).

Step 2

Microwave for one minute at 80% power (I have a 1,000 watt microwave; if your microwave has more or less watts, you may need to adjust the time a bit). The top will look light and yellow and may even seem undercooked but if you gently press the top and it lightly springs back, it's perfect (don't overcook or it will be dry and tough in spots).

Step 3

Serve warm with a scoop of vanilla ice cream, if desired.