French Onion Soup

Yes, prepare through step 9 (broth is done simmering) and refrigerate up to 3 days, or freeze up to 2 months. Reheat gently on the stovetop, then finish with the bread and cheese toasts under the broiler as directed in steps 11–14.

Regular yellow onions work perfectly—this recipe calls for them. Sweet onions (Vidalia) can be used but are less sharp; avoid red onions, which don't caramelize the same way.

Rushing the caramelization by using too-high heat, resulting in burnt rather than caramelized onions (they taste bitter and acrid instead of sweet and deep). Cook on medium heat for 45 minutes, stirring often, letting the onions darken gradually. This cannot be rushed.

Gruyère is traditional for its nutty flavor and melting quality, but Swiss, Emmental, or a mix of Gruyère and Parmesan work. Avoid cheddar, which can become stringy and separate; use cheese that melts smoothly and browns nicely.

Caramelizing onions in a slow cooker does not produce the same deep color or flavor—the low, moist heat steams rather than caramelizes. Do caramelization on the stovetop, then transfer to a slow cooker on low for the 20-minute simmer if needed, but the stovetop method is superior.

Refrigerate the broth (without bread and cheese) in an airtight container up to 3 days. Reheat gently on the stovetop over medium-low heat until steaming. Make fresh bread toasts and top with fresh cheese, then broil as directed—reheated cheese can become tough and rubbery.