Caramelized onions and melted Gruyère are a heavenly match, so sandwiching them between crispy toasted bread is a sure win. This grilled cheese take on the classic French onion soup will make you wonder why you ever bothered with the broth.
The onions:
Caramelized onions aren’t difficult to make, but they can’t be rushed. Keep the burner turned to medium-low and stir every once in a while, scraping the bottom of the pan and adding a tablespoon of water if the onions start to stick. Don’t be tempted to hurry them by turning up the heat; the moment the onions start to sizzle aggressively, they’re frying, not caramelizing. They’ll definitely brown faster, but they won’t have that beautiful sweetness and luscious jammy texture. You can’t fast-track flavor.
The ratios:
A sandwich requires thoughtfully balanced ingredients and careful construction, and this French onion grilled cheese is no different. During development, I experimented with different ratios of bread, cheese, and onions, and found that pairing 1/4″ slices of bread with 1 oz. Gruyère and 1/4 cup caramelized onions produced the ideal balance of flavor and texture for myself and taste-testers. Of course, taste is subjective, and if you prefer more cheese or a bigger pile of onions, it’s your sandwich. Go wild.
Storage:
Grilled cheese is always best fresh, but if you want to work ahead, the caramelized onions can be made up to three days in advance. Store in an airtight container in the refrigerator. Just make sure they come back to room temperature before you use them—if they’re cold, they’ll prevent the cheese from melting!
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