Cheesy Caramelized Onion Tart Recipe

Caramelizing onions is the perfect way to take an ordinary, humble ingredient and, with a bit of patience, transform it into an irresistible mixture of rich, buttery, salty, and sweet goodness that melts in your mouth. Put those onions on a tart, and you really don't need anything else to make it a showstopper.

Recipe developer Michelle Bottalico has created a recipe for a cheesy caramelized onion tart that takes those delicious onions, which can hold up the tart on their own, and pairs them with Swiss cheese, Parmesan, and chives for a subtle flavor boost. Allow enough time to prepare the onions, because they cook slowly, but the end result is definitely worth it. Plus, a frozen puff pastry sheet makes this recipe come together more effortlessly. The result is a crispy, flaky crust topped with melted cheeses and those rich and creamy onions that is sure to become a favorite at your next get-together.

To make this recipe, you will first need to caramelize some onions, and you will need butter, olive oil, Vidalia onions, salt, and pepper for that step. Pick up a puff pastry sheet from the freezer aisle, and make sure to thaw it before starting to make the tart. You'll also need Swiss cheese and Parmesan cheese to add more flavor to this dish, as well as fresh chives to sprinkle on top before baking.

Place butter and olive oil in a large pan with deep sides over medium heat.

Once butter is melted and bubbly, add onions and cook, stirring occasionally, for 7-8 minutes until translucent. Add salt and pepper, and stir.

Lower heat to medium-low and cook for an additional 30 minutes, stirring occasionally to prevent sticking, until onions are soft and browned. If all the liquid evaporates, add water 1 tablespoon at a time to prevent the onions from burning. Lower the heat a little if necessary.

Taste and adjust for salt if necessary.

Preheat oven to 400 F.

Unroll puff pastry sheet and place onto a parchment-lined baking sheet.

Fold in all 4 sides about ½ inch and press gently to form finished edges. Prick the bottom all over with a fork.

Evenly distribute the Swiss cheese on the pastry sheet, followed by the Parmesan cheese.

Arrange the onions in an even layer on top of the cheese.

Sprinkle the chives on top of the onions.

Place the baking sheet in the oven and bake for 20-23 minutes until the pastry crust is lightly browned and cooked on the inside and the cheese is melted and hot.

Let cool for about 5 minutes before slicing and serving. The tart can also be served at room temperature if desired.

This recipe contains a pleasing combination of ingredients, but the truth is, there's not only one way to make this delicious onion tart. It's highly customizable depending on your tastes and what you have on hand. Vidalia onions are a good choice for caramelized onions because of their sweet and mild flavor, but you can use other kinds of sweet onions with good results, or even regular yellow or red onions. Some people like to add a couple teaspoons of sugar along with the salt for a sweeter taste, but that is up to you. Onions can be caramelized in butter, olive oil, or both, so feel free to switch it up if you prefer one or the other. Just keep the overall quantity the same.

You can't go wrong with many different kinds of cheeses in this recipe. If you don't have Swiss, you could try Gruyére, Gouda, or feta. For a stronger taste, you could even use blue cheese or Gorgonzola if you like a pungent flavor. 

A little water is added to the pan if the onions start to stick in order to keep them from burning. If you want to go for a stronger taste reminiscent of French onion soup, you could use beef broth instead. Lastly, many kinds of fresh herbs would work well here, so if you don't have chives, you can use a different kind depending on what's available.

Yes, you can make this caramelized onion tart ahead of time to fit your schedule better. You have two options depending on what works best for you. The first is to make the whole tart ahead of time. You can serve it at room temperature if the waiting time wasn't that long, or you can store it in the fridge for up to 4 days. Bring the tart back to room temperature before eating it, or reheat it in the oven right before serving.

The second option is to only caramelize the onions ahead of time and then assemble and bake the tart before serving. The onions are the most time-consuming part of the preparation, so this is a good option if you're pressed for time the day you plan to enjoy it but still want to serve a freshly baked dish. Caramelized onions will keep in an airtight container in the refrigerator for up to 7 days, or in the freezer for 6 months.