Vermicular | French Onion Soup (14cm)

Ingredients

• 1 large onion, thinly sliced against the grain
• ⅔ tablespoon unsalted butter
• ⅓ teaspoon kosher salt
• 1 bay leaf
• 1 cup beef broth
• Salt and freshly ground pepper, to taste
• 2 slices baguette, buttered and toasted
• Grated Gruyere cheese