INGREDIENTS
•
1/2 cup (1 stick) unsalted butter
•
2 pounds yellow onions (about 6 medium), halved and thinly sliced lengthwise
•
8 to 10 sprigs fresh thyme
•
1 teaspoon kosher salt, plus more for seasoning
•
1 teaspoon freshly ground black pepper, plus more as necessary
•
1 tablespoon flour
•
1 cup dry white wine
•
4 cups beef stock or low-sodium beef broth
•
2 cups chicken stock or low-sodium chicken broth
•
1 1/2 cups cubed ciabatta bread
•
3 cups grated Gruyere cheese