Onion soup is Holy Writ. Just ask anyone old enough to have made the midnight pilgrimage to Les Halles, the old central market of Paris, to have a bowl of cheese-topped soupe a l’oignon under the giant iron and glass pavilions filled with produce being pushed around by burly fellows (les forts des Halles) who took time off from their work to mock tourists or to couple with the putes hanging out nearby on the boulevard de Sebastopol or operating out of the dingy hôtels de passe on the narrow rue Ouincampoix. Long since torn down, the market has moved out to suburban Rungis, where no one has ever gone for fun, to be replaced by the Pompidou Center’s forced postindustrial gaiety. Because of the cheese melted over it, the Halles-style onion soup is familiarly called a gratinée. I’m all for getting rid of that ropy yellow toupee, and I find myself opting for unbrowned onions and chicken stock instead of the brawny darkness of the classic. But I will not try to impose this personal taste on you (the recipe is classic but offers options that will lead to a lighter soup).
You might also want to think about making a complete Halles meal, a real blast from the past, starting out with what habitués called “un demi, demi” a half dozen snails and a glass of beer (in theory a half liter but normally much less).