When I posted a photo of this sandwich on social media, the purpose was to inspire people to use leftovers in creative ways. I just figured, if you have leftover caramelized onions, some cheese, some bread, and you know how to make a grilled cheese, then make a French Onion Grilled Cheese! However, many people have messaged me for a recipe since I posted the photo, and I aim to please -- so here it is!
Note: If you don't happen to have caramelized onions on hand like I did and you want to make some, I suggest making a large batch (at least 5 or 6 onions) and plan to use them throughout the week for other meals. It's such a time consuming process, so you may as well! Yes, there are several recipes out there including shortcut methods, but I still prefer to cook them low and slow. I'll eventually write a separate post for this, but for now I'm just going to put it here:
- 5 to 6 sweet onions, sliced in half from root to end, then each half sliced to desired
thickness from root to end (I use sweet onions so no added sugar is necessary)
- 1 Tbsp extra virgia olive oil
- 1 Tbsp butter
- kosher salt
- water, as needed
- 1 to 2 Tbsp apple cider vinegar, to use at the end for deglazing
In a large skillet over medium high heat, add the oil and butter. When the butter has melted, add the onions and distribute them evenly in the pan. Let them cook for about 2 minutes without stirring. Stir them around a bit, then cook for another few minutes without touching them. Turn the heat down to medium or medium-low, sprinkle some salt over the onions, and continue cooking until they get dark brown and caramelized. Stir them every few minutes during the cooking time, but not too often or the natural sugars in the onion won't have a chance to brown. Definitely give them a stir before they burn, and feel free to splash a little water (1 Tbsp at a time) into the pan as needed to help loosen the bits and keep the onions from drying out. This process can take anywhere between 45 minutes to an hour and a half. At the very end of cooking, once you've received your desired level of caramelization, add the apple cider vinegar to deglaze the pan a final time and allow it to cook an extra minute. Use immediately or let cool and store in the fridge for up to a week. Makes about 2 cups.
Ingredients
Per sandwich:
2 slices of hearty bread
Softened butter
1-2 oz of gruyere cheese, grated
2 Tbsp caramelized onions, reheated (recipe above if you don't already have some)
Fresh thyme leaves, chopped (if desired)
Directions
Heat a large skillet over medium high heat. Spread a generous amount of the softened butter on one side of each bread slice. Be sure you cover the entire side - no dry spots! If I have it, I like to use Japanese style bread like this because of it's density and perfectly square shape. But any dense bread will do.
Place the bread butter-side down in the skillet. Sprinkle the cheese on both sides of the bread, followed by the thyme leaves. Spoon the caramelized onions on one of the slices. If the buttered side starts to get too brown before the cheese has had a chance to start melting, then lower the heat.
When the cheese has started to melt on the slice without the onions, use a spatula to carefully flip it onto the other slice and gently press so that the cheese sticks to the onions. Flip the sandwich over and press again. Remove to a cutting board and slice in half diagonally.
If you're making several sandwiches, you can place the sandwiches on a cookie sheet as you finish making each one and keep them warm in the oven at 200°F for 15 to 20 minutes.
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