Has anyone else tried it?

Basically, you just sit your mayonnaise in a window sill that receives direct sunlight for at least 3 weeks, the longer/hotter the better. It's generally a good idea to leave the cap off so the mayonnaise can ferment better, but it's smell might get a bit overbearing for some.

That's basically all there is to it, you'll have some delicious fermented mayonnaise. I've tried some, and it's AMAZING. Literally one of the best things you'll try this year.