Balsamic Caramelized Onion and Brie Crostini

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I first made these little beauties a few years back for a Superbowl party. I knew that I loved caramelized onions and that I also loved Brie, so I threw caution to the wind and gave these a go, and it was love at first bite. I have made them a few times since then for holiday parties and each time I do, my love grows stronger.

I wish I could say that I made them this past weekend for a swanky dinner party that I hosted, but I want us to have an honest relationship. I want you guys to trust me. The truth is that I was sitting at work, trying to decide what to make for dinner, when suddenly I heard the siren song of the caramelized onion and brie crostini. And when the caramelized onion and brie crostini sirens start singing, you listen. So I hit up the supermarket on my way home from work and whipped these guys up for dinner.

The recipe below makes a good amount of crostinis, but the good news is that the ingredients keep really well overnight. Just store everything in separate airtight containers and then assemble and bake as you normally would when you’re ready to eat them the next day (or even the day after that!). The only downside to the recipe is that the caramelized onions take a while to prepare, but it’s not a lot of hands-on prep – for the most part, they’re just cooking away in the frying pan and you can go about your business elsewhere as long as you check in on them from time to time. And I know that it seems like a ton of onions while you’re chopping them, but you will be amazed at how much they cook down. Amazed, I tell you!


Aside from caramelizing the onions, the process is pretty simple. Once you make your crostinis by slicing, olive oiling/salting, and baking your baguette, it’s just a matter of stacking the onions and brie on each crostini and putting them back in the oven for a few minutes. Easy peasy!

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Balsamic Caramelized Onion and Brie Crostini
makes: 30-35 crostinis / prep time: 1 hour

For the caramelized onions:

  • 3 large sweet onions, cut in half and sliced
  • 2 tablespoons olive oil
  • 2 tablespoons brown sugar
  • 1/2 cup water, divided
  • 1 tablespoon balsamic vinegar
  • 1/2 teaspoon salt

Heat the olive oil in a large skillet over medium heat. Add the onions and cook for 15 minutes, or until soft and slightly transparent. Add the brown sugar and cook covered, stirring occasionally, for another 20 minutes, or until golden brown. Add 1/4 cup water, cover, and cook for another 15 minutes, stirring occasionally. Add the balsamic vinegar, salt, and remaining 1/4 cup water (or less, if liquid remains from the last step) and cook, covered, until the liquid is absorbed, stirring occasionally.

For the crostinis:

  • 1 French baguette, sliced
  • 1/2 cup olive oil
  • salt to season

Preheat your oven to 350 degrees. Arrange the baguette slices on baking sheets. Brush both sides with olive oil and sprinkle with salt. Bake until golden, about 15 minutes, rotating the sheets halfway through baking.

Once the onions have finished cooking, arrange a spoonful on each crostini and top with a slice of Brie. Bake at 350 degrees until the Brie is melted, about 12 minutes.

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