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French Onion Grilled Cheese Sandwich

French Onion Grilled Cheese Sandwich with melty Gruyere and caramelized onions make the best comfort food. It has all the flavors of a classic French onion soup, but quicker to make and portable! Your taste buds will swoon!
5 from 30 votes
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  • 4 slices sourdough bread or cheese bread
  • 1 small sweet onion thinly sliced
  • 2 teaspoons whole-grain mustard
  • Generous pinch of salt
  • 1 teaspoon fresh thyme
  • 4 tablespoons beef stock or balsamic vinegar
  • 1 cup grated Gruyere cheese
  • 2 tablespoons olive oil
  • 2 tablespoons unsalted butter


Caramelized onions

  • Coat the bottom of the pan with olive oil and heat the pan on medium high heat until the oil is shimmering. Add the onion slices and stir to coat the onions with the oil. Spread the onions out evenly over the pan and let cook, stirring occasionally for 10 minutes. Sprinkle some salt and pour the stock. Continue stirring until onion caramelize into a beautiful deep golden brown. Set aside.

Grilled cheese sandwich

  • Spread the butter and whole grain mustard on one side of each piece of bread. Add turkey, caramelized onions, grated Gruyere on the inside of the bread and top with second piece of bread that is spreaded with the butter and grain mustard
  • Melt butter in a skillet over medium until beginning to foam. Add prepared sandwich and turn heat on to low. Make sure that you aren’t burning the butter and flip as soon as one side is golden brown and continue with other side. This process should take 8-10 min on each side