As sandwiches go, the grilled cheese is one of the simpler ones. It’s also one of the best — a near-perfect use of two slices of bread. This grilled cheese is particularly indulgent: We use thick-cut artisan bread slathered in mayonnaise, which fries up with a crispy, golden brown crust and a soft, chewy middle. And between those slabs of toast? Creamy, nutty Gruyère, and oodles of jammy caramelized onions.

The downfall of any grilled cheese is, of course, partially melted cheese; you need that gooey, satisfying cheese pull with every bite. So with this recipe, we stir the grated Gruyère in with the hot, hot onions before layering it on the bread, so the cheese melts evenly throughout, and fills in all the nooks and crannies between the onions. In other words: the cheese to onion ratio is spot on.

We love how buttery and rich this grilled cheese is — it’s greasy in all the right ways. It’d make for a truly sublime midnight snack (and, frankly, a darn good hangover cure), or a perfectly unfussy weeknight dinner. In the test kitchen, a bunch of us ate it for breakfast and couldn’t have been happier. What we’re saying is: this grilled cheese transcends the lunch hour.

Our tip: if you want to zhuzh up this grilled cheese even more, we recommend adding arugula, fig or raspberry jam, and Dijon mustard.

Servings: 2

Ingredients

2 Tbsp unsalted butter

1 lb sweet onions, halved and thinly sliced

2 tsp sherry vinegar

5 oz Gruyère cheese, grated

4 slices artisan bread, cut no wider than 1” thick

¼ cup mayonnaise, divided

Directions

1. In a large skillet over medium-high heat, melt the unsalted butter. Add the onions, cover, and cook, stirring once or twice, until the onions are softened, 3 to 5 minutes.
2. Remove the lid, reduce the heat to medium-low, and cook, stirring occasionally, until the onions are a deep golden brown, 20 to 25 minutes.
3. Deglaze the skillet with the sherry vinegar and cook until the liquid has evaporated, about 1 minute. Transfer the onions to a medium bowl. Clean the skillet, and set it aside.
4. Add the Gruyère cheese to the onions and stir to combine. Divide the mixture between 2 slices of the artisan bread, and then top with the remaining slices.
5. Heat the skillet over medium heat. Spread 2 tablespoons mayonnaise on the top pieces of bread, making sure to cover the edges.
6. Transfer one sandwich to the skillet, mayonnaise-side down. Press down gently on the sandwich to make sure all points of the bread are touching the skillet. Cook the sandwich for 2 to 3 minutes, pressing down occasionally, until the bread is golden brown.
7. While it’s cooking, spread 2 tablespoons mayonnaise on the top slice of bread. When it’s ready, flip and cook 2 to 3 minutes more, until the bread is golden brown and the cheese is melty.
8. Transfer the grilled cheese sandwich to a plate. Repeat steps 6 and 7 with the second sandwich. Serve hot.

Recipe source: The New York Times

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