Did you know that caramelized onions and cheese are best friends? Honestly, this simple combination is to die for.
Ingredients
1 tablespoon extra-virgin olive oil
1 large yellow onion (1 pound), thinly sliced
1/8 teaspoon fine salt
1 tablespoonrice vinegar, preferably unseasoned
3 tablespoons unsalted butter, at room temperature (may substitute vegan butter, such as Miyoko)
2 teaspoons white or dark miso paste
1 tablespoon whole-grain mustard
4 slices good-quality sandwich bread
4 ounces grated Gruyère cheese (1 cup; may substitute vegan shredded cheese, such as Violife or Daiya)
Cornichons (a.k.a. gherkins), for serving (optional)
Directions
Step 1
In a large skillet over medium-high heat, heat the oil until shimmering. Add the onion and salt and cook, stirring often, until they start to soften and brown, 5 to 6 minutes. Reduce the heat to medium-low and cook, stirring occasionally, until the onions are deeply browned and sticky, 30 to 45 minutes. Stir in the vinegar. Transfer the onions to a small bowl.
Step 2
In a small bowl, mix 1 tablespoon butter with the miso paste and mustard. Spread one side of each bread slice with the remaining 2 tablespoons butter. Spread the other sides with the miso butter.
Step 3
Return the skillet to medium-low heat. Place two of the bread slices, plain-buttered-side down, in the skillet. Divide the cheese and onions evenly between them and top with the other bread slices, plain-buttered-side up. (You want the miso butter on the inside of the sandwiches.) Cook until the bread is golden brown, 5 to 7 minutes. (Resist the urge to press the sandwich with a spatula.) Flip the sandwiches over and cook on the other side until the bread is golden brown and the cheese is melted, 5 to 7 minutes. Transfer to plates and serve with cornichons, if desired.
https://www.washingtonpost.com/recipes/caramelized-onion-grilled-cheese-sandwiches-miso-butter/