French Onion Grilled Cheese: A Eureka Moment

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If you like French onion soup and you like grilled cheese, you’ll love French onion grilled cheese. Our recipe takes the savory and gently sweet flavors to the next level. Don’t miss it. (Psst…you might like French onion soup potato skins, and our Hot Mess grilled cheese, too.)

grilled cheese with onions on a plate on a napkin

Why we love this recipe

Caramelized onions done right are absolute culinary magic. They have a deep, beautifully balanced sweet and savory flavor combo that just couldn’t be more enticing.

Grilled cheese speaks for itself where comfort is concerned. But like any staple recipe, it can be good, or it can be GREAT.

This best-in-class french onion grilled cheese sandwich recipe brings together the best elements of both worlds and really amps up the flavors.

adding shredded gruyere and cheddar, grated pecorino, caramelized onions, salt, and pepper to a small mixing bowl

Ingredients

Here’s what you’ll need to make this grilled cheese recipe:

  • Good-quality aged Gruyere cheese
  • Extra-sharp cheddar cheese
  • Grated parmesan or pecorino cheese
  • Fine sea salt (we like using truffle salt when we have it)
  • Freshly ground black pepper
  • Caramelized onions
  • Really good sourdough or rye bread
  • Dijon mustard
  • Salted, cultured butter
spreading dijon mustard and the cheese and onion mixture onto homemade sourdough bread

How to make a French onion soup grilled cheese

Here’s what you need to do to make this sandwich. You can see all the steps in action in the video that accompanies this post.

  • Grab a small mixing bowl and a fork to mix the filling ingredients together.
  • Shred the gruyere and cheddar, and grate the pecorino.
  • Mix up the gruyere, cheddar, pecorino or parmesan, salt and pepper, and caramelized onions. Tease the onions apart with the fork to make sure everything is mixed well.
  • Spread the mustard onto the inside faces of the bread slices.
  • Spread the cheese and onion mixture evenly onto one slice of bread and top with the other slice.
  • In a small frying pan, melt the butter over medium heat.
  • Place the sandwich into the pan and let the bottom slice of bread soak up some of the melted butter. Then carefully flip the sandwich and swipe it around the pan to mop up the remaining melted butter.
  • From this point on, the name of the game is to regulate the heat so that the cheese mixture melts in the same timeframe that the bread becomes golden-brown. You’ll have to use your judgment based on your own stovetop and pan, but this typically means keeping the burner on a medium-low setting.
  • From time to time, use your spatula to press down on the grilled cheese to make sure it’s melting and browning evenly. During cooking (which should take a total of about five minutes), flip the sandwich at least once more to brown the top side. You’re welcome to flip it more if it helps you achieve even melting and browning, but it shouldn’t really be necessary. Toward the end of cooking, you can lower the heat and place a lid on the pan to aid in melting if you like. Don’t leave it on for more than a minute or so, to ensure that the bread remains crisp and doesn’t steam.
  • When the cheese is melted and the bread is golden-brown, remove the grilled cheese to a cutting board or plate, cut in half, and serve.
cooking grilled cheese in a small pan

Protips

  • Shredding the cheese and mixing it up with the caramelized onions gives you a consistent, melty, gorgeous tangled mess in every bite.
  • If a little bit of cheese spills out the edges, that’s fine. It almost tastes better with a little bit of browned cheese around the edges. (If spillage doesn’t happen, that’s all good too.)
  • Use the best-quality ingredients you can find. Good bread, butter, and cheese go a long way in this recipe.
  • The quantities in the recipe below make one generous sandwich, but you can of course scale it up to feed your crowd.
closeup of grilled cheese with a bite taken out of it

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French Onion Grilled Cheese

French onion soup? Goooood. Grilled cheese? Goooood. French onion soup grilled cheese? Very, very good. Here's our best-in-class iteration of this mashup of classics. It's super-flavorful and incredibly satisfying, and it can be yours in about 10 minutes. Prepare a batch of caramelized onions in advance and use the rest in the other recipes suggested in that post.

Prep Time 5 minutes
Cook Time 5 minutes
Total Time 10 minutes
Serves 1

Ingredients

  • 1 ounce shredded gruyere cheese
  • 1 ounce shredded extra-sharp cheddar cheese
  • 1 tablespoon grated parmesan or pecorino cheese
  • Pinch of salt (we like using truffle salt when we have it)
  • A few grinds of black pepper
  • 1/4 cup caramelized onions
  • 2 slices sourdough or rye bread
  • 1 tablespoon Dijon mustard
  • 2 tablespoons salted, cultured butter

Directions

  1. In a small mixing bowl, use a fork to mix together the gruyere, cheddar, pecorino or parmesan, salt and pepper, and caramelized onions. You can gently tease the onions apart with the fork to make sure everything is mixed well.
  2. Spread the mustard onto the inside faces of the bread slices.
  3. Spread the cheese and onion mixture evenly onto one slice of bread and top with the other slice.
  4. In a small frying pan, melt the butter over medium heat.
  5. Place the sandwich into the pan and let the bottom slice of bread soak up some of the melted butter. Then carefully flip the sandwich and swipe it around the pan to mop up the remaining melted butter.
  6. From this point on, the name of the game is to regulate the heat so that the cheese mixture melts in the same timeframe that the bread becomes golden-brown. You'll have to use your judgment based on your own stovetop and pan, but this typically means keeping the burner on a medium-low setting.
  7. From time to time, use your spatula to press down on the grilled cheese to make sure it's melting and browning evenly. During cooking (which should take a total of about five minutes), flip the sandwich at least once more to brown the top side. You're welcome to flip it more if it helps you achieve even melting and browning, but it shouldn't really be necessary. Toward the end of cooking, you can lower the heat and place a lid on the pan to aid in melting if you like. Don't leave it on for more than a minute or so, to ensure that the bread remains crisp and doesn't steam.
  8. When cheese is melted and bread is golden-brown, remove the grilled cheese to a cutting board or plate, cut in half and serve.

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Did you make this recipe?

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