Combine the flour, cocoa powder, caster sugar, baking powder and salt in a mug.
Make a well in the middle and add the oil, milk and vanilla essence.
Mix to combine, making sure you incorporate all the dry ingredients.
Stir through some cherries, if using. Sprinkle the top of the mixture with a few chocolate chips, if using.
Microwave on full power for 40 seconds or until the edges are set but the middle is still gooey.
Take care while eating - it will be hot!