In a microwave-safe mug, whisk the egg with the granulated sugar until the sugar dissolves.
Add the milk and vegetable oil and whisk until combined.
Mix in the flour in two additions. Add the baking powder and instant coffee and whisk until combined.
Microwave for 1 minute 30 seconds at 960 W. In the video, this is power level P8 on a 1200 W microwave. Adjust cooking time to suit your microwave.
Check the centre with a toothpick; it should come out clean. Finish with a dusting of powdered sugar if desired.
Video
Notes
The video specifies 1 minute 30 seconds at 960 W. The card’s 2-minute cooking value is rounded up to a whole minute; use the method’s power setting and toothpick check when cooking.