Few combinations are as classic—or as comforting—as a warm bowl of soup and a sandwich grilled to perfection. Here we’ve combined the two with a recipe for French Onion Soup Grilled Cheese, a union that’s at once gooey, soupy, crunchy, and yes, incredibly cheesy. Gruyère and Fontina cheeses strike a harmonious chord with a sweet and savory onion compote, while a side of arugula delivers a healthy dose of bright green contrast.
Stir onions frequently to prevent them from burning.
To check if the pan is hot, carefully hover your hand a few inches away from the pan. When it’s hot, you’ll be able to feel the heat.
Rotate the bread slices in the pan so that they toast evenly throughout.
⅛ ounce thyme
2 yellow onions
1½ teaspoons butter
8 teaspoons mayonnaise, divided
4 slices sourdough bread
2 tablespoons flour
16 ounces vegetable stock
1½ teaspoons Dijon mustard
2 ounces shredded Fontina cheese
3 ounces shredded Gruyère cheese
5 ounces baby arugula
1 tablespoon olive oil
2 tablespoons water
10″ medium pan
12″ large nonstick pan
Strip thyme leaves, discarding stems. Peel onions, halve, and thinly slice. Halve lemon. In a large bowl, whisk together juice of 1 lemon and 1 tablespoon olive oil to make dressing. Season with⅛ teaspoon salt and pepper as desired and set aside.
Heat butter in a medium pan over medium-high heat. When butter is foamy, add thyme and onions and cook, stirring occasionally, until light brown and softened, about 7 minutes (see Recipe Tip). Add 2 tablespoons water and reduce heat to medium. Cook, stirring continuously, until onions are golden brown and very soft, about 5 minutes more.
While onions cook, place bread slices on a clean dry surface. Spread 2 packets mayonnaise evenly over tops. Heat a large nonstick pan over medium-high heat (see Recipe Tip). Once pan is hot, add bread slices mayonnaise-side down and cook on one side until bottom is slightly toasted, 2-3 minutes. Remove bread from pan and set aside to cool, toasted-side up.
Add flour to pan with onions over medium heat and stir vigorously until flour is no longer visible, 1 minute. Add vegetable stock. Increase heat to high, bring to a boil, then reduce heat to medium-high and simmer, stirring occasionally, until sauce is thickened and reduced by ¼, 4 minutes. Season with ¾ teaspoon salt and pepper as desired. Divide half of gravy between 2 bowls and cover with foil. Cook remaining gravy until reduced by half, 5 minutes more. Remove pan from heat.
Flip bread toasted-side down and spread remaining 2 packets mayonnaise evenly over tops. Flip bread and spread mustard evenly over toasted side. Divide half of cheese mix between 2 bread slices. Spoon onion gravy from pan over cheese, dividing evenly. Top with remaining cheese mix and remaining bread slices mustard-side down.
Return nonstick pan from bread to medium heat. Once pan is hot, add sandwiches and cook until bread is golden and cheese is melted, about 4 minutes per side. Divide grilled cheeses between 2 plates, cut in half, and serve with French onion soup. Add arugula to bowl with lemon oil dressing, toss to coat, and serve with soup and sandwiches.
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