last updated on October 29, 2026

I have been on a grilled cheese KICK recently and I am not mad about it because this caramelized onion grilled cheese smacks. The caramelized onions takes the grilled cheese to the next level! You will never go back to normal grilled cheese, I promise.

There is a long way and a quick way to caramelize onions, and I always do the quick way. And they taste incredible, so it is very worth the time saved! Here is how to quickly caramelize onions:

Chop the onions into thin pieces
Add the onions to a large pan or cast iron skillet with some butter.
Let the onions cook, stirring, until they begin to stick to the pan.
Pour a splash of water into the pan to deglaze the onions and let them continue to cook.
After a few minutes, add another splash of water.
Continue this process for about 10-15 minutes until the onions are caramelized!

If you like this caramelized onion grilled cheese, check out my other grilled cheese recipes!

Ingredients

2 tbsp butter
1 onion
1/4-1/3 cup water
4 slices bread
1 cup mozzarella cheese
2 tsp red pepper jelly optional

Instructions

Cut the onion in half, then into long slices. Add 1 tbsp butter to a large pan or cast iron skillet over medium heat. When the butter melts, add the onion. Let the onion cook for 3-4 minutes, stirring occasionally.
When the onions start to stick to the pan / brown, add 1-2 tbsp of water and continue to stir. This will deglaze the onions from the pan and add steam for the onions to continue to cook. After a few more minutes, add another splash of water. Repeat this process until the onions are golden brown and caramelized. This should take 10-15 minutes. Take the onions off the heat.
In a pan, add the remaining 1 tbsp of butter. Add one slice of bread, top with half the mozzarella, and a big scoop of the caramelized onions. Top with another slice of bread. Cook on both sides for a couple minutes until golden brown and until the cheese has melted.
If using, add red pepper jelly to each sandwich. Enjoy!

What’d you think? I’d love to hear your thoughts or if you have any questions!