01.  In a large Amazonía mug, mix together the flour, sugar, cocoa powder and, if desired, chocolate chips.

02.  Add the egg, milk and vegetable oil to the dry mixture and mix well until smooth.

03.  Microwave for 1-2 minutes, until the cake is cooked (the time may vary depending on the power of the microwave).

04.  Leave to cool slightly before serving, and enjoy this quick and delicious cake!