My friend’s mom loved this soup when she lived in England and begged the pub owner for the recipe. He refused to divulge it until the day she left the country. I have adapted it a little to keep his secret safe. Instead of the dark broth associated with a French onion soup, this recipe produces a broth with a lighter color. Makes 6 large bowls.
4 tablespoons unsalted butter
3 pounds yellow onions, thinly sliced
Pinch of kosher salt, plus more for seasoning
6 cups homemade chicken stock or good-quality canned chicken broth
1 tablespoon all-natural bouillon paste
1 tablespoon rice wine vinegar
Freshly cracked pepper to taste
2 cups (8 ounces) shredded Gruyère cheese
Preheat oven to 400 degrees F. Spread bread cubs out in a single layer on a baking sheet, and toast in the oven for 10 minutes. Remove from oven and set aside.
In a large pot set over medium-low heat, melt butter and add onions with a pinch of salt. Cover partially with a lid and let cook, stirring frequently, until onions are very tender, about 15 minutes.
Add chicken stock, bouillon paste, and vinegar. Let simmer for 1–2 minutes, and taste for seasoning. Add more kosher salt if needed, and cracked pepper.
Ladle soup into ovenproof mugs or bowls set on a baking sheet, and top with the sourdough croutons and a handful of cheese on each serving.
Bake until cheese starts to bubble and turn golden brown. Serve hot.
Reprinted with permission from Celebrate Every Day: Recipes for Making the Most of Special Moments with Your Family, by Jaime Richardson © Lyons Press.