In a microwave safe mug, mix together the flour, sugar, cocoa powder, baking powder and salt. Add in the egg, milk and oil. Mix until smooth.
Microwave on high for one minute. Remove from microwave and press in the rolo chocolate to the centre of the mug cake. Microwave for an additional 30 seconds. If not done, microwave in 30 second intervals until done.
Notes
Microwaves vary. You can tell that the cake is done if the top is no longer wet.
Best enjoyed immediately.
I like using avocado oil for this recipe, but any neutral oil works well.