Mix well until a smooth, thick batter forms. Scrape the sides and bottom of the mug to fully combine.
Let the batter rest for 30 seconds. This helps the oat flour hydrate and improves texture.
Place the mug in the microwave and cook on high for 60 seconds.
Check the center. If still slightly wet, microwave in 15-second intervals until just set.
Remove carefully, as the mug will be hot, and allow the cake to cool for one minute.
