Grilled Gruyere and Sweet Onion Sandwiches

Let’s elevate the humble grilled cheese sandwich and make Grilled Gruyère and Sweet Onion Sandwiches.  Everyone loves grilled cheese but they will swoon over this combination of caramelized onion, melty Gruyère cheese, crunchy whole-grain bread, Dijon mustard and prosciutto (which is optional, but I highly recommend it)!

To begin this recipe, you need to caramelize the onions.  This isn’t difficult but it takes a while.  Just cook the onion in butter and oil in a covered skillet until it’s softened.  Then uncover and continue to cook until the onions are dark brown and caramelized.

Find yourself a nice crunchy whole-grain bread.  This will make a lovely difference with this recipe.  Too soft of a bread will possibly cause it to fall apart so play it safe and go for crunchy!

On one side of each slice of bread, spread the remaining butter.  Flip the bread over and top the unbuttered side with mustard, onions, Gruyère cheese and prosciutto, if you are using it. Close the sandwiches and grill the sandwiches over low heat until the bread is toasted and the cheese is melted.  This takes about 10 minutes.  Flip the sandwiches about halfway through.

Cut the sandwiches in half, serve and eat!  Easy peasy??

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Grilled Gruyere and Sweet Onion Sandwiches

Makes: 4 sandwiches

Prep Time: 10 minutes

Cook Time: 35 minutes

Total Time: 45 minutes


  • 3 tbsp unsalted butter, softened
  • 1 tbsp extra-virgin olive oil
  • 1 large onion, halved and thinly sliced crosswise (4 cups)
  • Salt and freshly ground pepper
  • Eight 1/2-inch-thick slices of whole-grain bread
  • Dijon mustard
  • 8 ounces imported Gruyère cheese, thinly sliced
  • 4 thin slices prosciutto, optional


In a deep skillet, melt 1 tablespoon of the butter in the oil. Add the onion, cover and cook over high heat, stirring once or twice, until softened, about 5 minutes. Uncover and cook over moderate heat, stirring occasionally, until the onion is very tender and caramelized, about 25 minutes longer. Add water to the skillet as necessary, 1/4 cup at a time, to prevent the onion from scorching. Season the caramelized onion with salt and pepper.

Spread the bread with the remaining 2 tablespoons of butter and arrange, buttered side down, on a work surface. Spread a thin layer of mustard on each slice. Top half of the slices with the onion, Gruyère and prosciutto, if using, and close the sandwiches.

Preheat a skillet or panini press. Grill the sandwiches over low heat until the bread is toasted and the cheese is melted, 10 minutes. If using a skillet, press the sandwiches with a spatula and flip them halfway through. Cut in half and serve right away.

Recipe adapted from Food & Wine


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    Recipe Reviews

    • Harry

      I can see that the food will be delicious, for this longer and colder than normal, Winter this year. Thanks Fran, for this hardy sandwich. I’ll add variety to my diet this Fall going into Winter. Cheers

      • Francine

        I hope you love these!

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