Soupe à l’oignon gratinée

Comfort food at its soulful best, few things are as gratifying to make and eat as onion soup. Ever since acquiring the appropriate pot-bellied narrow-mouthed serving vessels (lion's head motif charming, if optional), I'm convinced it's all about proportion. What Phi is to Greek architecture, the pleasing balance of onions-to-broth-to-croutons-to-cheese is to French onion soup. And without the perfectly proportioned bowl, this golden ratio is virtually impossible to achieve.

The method I've been enamoured with as of late comes from Thomas Keller's powerful paen to bistro cookery, Bouchon, in which the simple is made sublime thanks to relentless refinement of technique. The most critical thing is the cooking of the onions. Caramelising merely the cut surfaces of the julienne won't do; to tease forth depth of colouring and nuanced sweetness - the result of natural sugars being gradually broken down and releasing their complex flavour compounds - the entire julienne right to its very core needs to be evenly caramelized. To this end, only very slow heat (about 5 hours in an enamelled cast iron pot over the merest flame and a diffuser) will do. After this, good beef broth, slowly crisped croutons, and a cap of aged Comté, molten beneath its gratineed crust, ensure good eating.