Step by step

Heat the red onion in a frying pan with a dash of olive oil

Tips
If you don’t have any brandy in the house you could use something else, such as white wine or marsala. With the former you’ll get a drier finish, with the latter you’ll have a somewhat sweeter and more aromatic sauce.
Trivia
Here’s a recent discovery about the red onion: it is rich in nitrogen oxide, an agent involved in obtaining an erection.