Molly Stevens is a great cook, so it makes sense that she’s a food writer and cookbook author, too. But she also has an intuitive palate and a breadth of culinary knowledge. And she learned to cook in France. This recipe is a favorite. “Although slicing onions by hand gives you the most consistent and best results,” Molly says, “I admit to using a food processor to get through the heaps needed to make this soup.” Two more tidbits of advice: “It may seem that you have far too many onions, but don’t worry – they’ll cook down to about a quarter of their original volume … You want the toasts to cover almost all of the surface of the soup, but don’t overlap the slices too far or you’ll have too much bread.”
In a large, wide soup pot, melt butter over medium heat. Add onions and season with salt and pepper to taste. Cook gently, stirring frequently, until onions are very soft and have begun to turn a deep blond shade, about 40 minutes. (It’s important to avoid browning them.) Stir in flour and cook 3 to 4 minutes, stirring frequently. Pour in wine and increase heat to medium-high, stirring and scraping the bottom of the pot to loosen any caramelized juices. Cook until liquid is almost completely reduced. Add stock.
Tie herbs together with string or place inside a piece of cheesecloth. Add herb bundle and bring to a simmer. Season lightly with salt and pepper and simmer 20 to 30 minutes. Onions should be soft but not falling apart. (You may make this soup ahead to this point if you like, and hold it for several hours or even a few days before serving.) Just before serving, heat oven to 350 degrees. Arrange baguette slices on oven rack. Toast lightly, 7 to 10 minutes, and set aside. Increase temperature to 450 degrees. Set six ovenproof crocks on a heavy baking sheet, and ladle hot soup into them. (Discard herb bundles.) Float toasts on soup and top each with a handful (¼ cup) of Gruya¨re.
Bake until cheese is melted, bubbly, and barely golden, 10 to 12 minutes. Serve immediately when cheese is gooey and crocks are hot.