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Is there nothing better than caramelized onions?
Yes, they take some time to make, but they’re not hard to cook, and it’s so so worth the effort.
Here is great way to enjoy them—in a simple rustic tart, with some shredded Gruyere cheese and a sprinkling of thyme.
You can either use a ready made frozen crust (the flat or folded kind), or make your own crust.
Rustic Onion Tart Recipe
Ingredients
- 1 recipe for butter sour cream pastry dough* or 1 packaged, flat pie crust (Trader Joe's has one in their frozen section)
- 3 medium sized red and/or yellow onions (enough for 5 to 8 cups, sliced)
- 2 tablespoons extra virgin olive oil
- 1 tablespoon butter
- Salt
- 1 teaspoon balsamic vinegar
- 1/2 teaspoon fresh thyme, chopped, or 1/4 teaspoon dried thyme
- 3/4 cup (not packed) roughly grated Gruyère Swiss cheese
*Sour cream pastry dough:
- 1 1/4 cup (160 g) all purpose flour
- 1 teaspoon salt
- 5 ounces of butter (1 1/4 sticks, 10 Tbsp, 137g), cubed
- 1/4 cup sour cream
Method
1 Prepare the dough: If you are making a crust from scratch, prepare the dough and let it chill in the refrigerator while you are cooking the onions.
To prepare the dough, whisk the flour and salt together in a large bowl. Cut the butter into the flour with your hands or with a pastry cutter, until the mixture resembles a coarse meal.
Add the sour cream and use a fork to incorporate it into the dough. Gather the dough into a ball and shape it into a disk. Wrap it with plastic wrap and chill for at least an hour.
2 Peel and slice the onions, lengthwise from stem to root. (See How to Slice an Onion)
3 Caramelize the onions: Heat olive oil and butter in a large, heavy-bottomed sauté pan on medium heat. Once the butter has melted, add the onions and sprinkle a little salt over them.
Cook, stirring occasionally for 10 minutes, until the onions have softened and are translucent.
Reduce the heat to medium low and cook for an additional 40 minutes, stirring occasionally, until the onions are well browned.
Add balsamic vinegar and cook for 10 minutes more, until onions are completely caramelized. Remove from heat.
4 Roll out the dough: Preheat the oven to 450°F. Remove the dough from the refrigerator and let stand for 5 minutes before rolling it out.
Roll out the dough on a lightly floured surface to a 13-inch diameter. Transfer the crust dough to a cookie sheet lined with parchment paper.
5 Layer the cheese and onions onto the dough: Place all but a couple tablespoons of the cheese in the center of the dough. Spread to within 1 1/2 inches from the edges. Add the caramelized onions, layering them on top of the cheese. Sprinkle with thyme.
6 Pleat the edges: Fold the edges of the crust dough over so that a small circle of onion is still showing in the centre of the tart. Sprinkle the remaining cheese over the top of the tart.
7 Bake: Place in the oven on the middle rack. Bake for 10 minutes at 450°F. Reduce the heat to 350°F and bake for an additional 20-25 minutes, until the crust is golden brown.
Remove from oven and let sit for 10 minutes before serving.
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Elise Bauer is the founder of Simply Recipes. Elise launched Simply Recipes in 2003 as a way to keep track of her family's recipes, and along the way grew it into one of the most popular cooking websites in the world. Elise is dedicated to helping home cooks be successful in the kitchen. Elise is a graduate of Stanford University, and lives in Sacramento, California.
Rustic Onion Tart
Wow! I followed the directions(except for using nonfat plain Greek yogurt instead of sour cream). What a satisfying, delicious savory tart. I would love to learn a less buttery version of the crust, even tho it will sacrifice taste. I will try, as other reviewers, other fillings for this. Yumm! Such a nice treat for using the fresh crop of onions on the farm stand next door right now!
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This tart is always served to rave reviews! For the crust, when I don’t have sour cream, I will substitute plain yogurt or buttermilk. I also use whatever veggies and cheese I have on hand for the filling and vary the herbs used. Today’s will include bell peppers, tomatoes, zucchini, and onion. I precook the hard veggies (bell peppers and onion). I drain the zucchini and tomatoes so they don’t make the crust soggy, put them raw on the crust with the cooked onions and bell peppers, and cook them in the oven as directed.
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Wonderful Maria! Thank you for sharing your modifications. It’s always helpful to see how flexible a recipe can be.
Hi what other cheeses can you use?
Hi Karen, you could substitute with grated Comté, Emmentaler, or Gouda. Or you could sprinkle with a little blue cheese, goat cheese (chevre) or feta.
I love this tart, it’s fabulous, a crowd pleaser! I’d like to freeze it, could you tell me if it is best to freeze it before baking or already baked? Thanks.
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Hi, Angela! We haven’t tried freezing this tart, but my instincts say that it should do just fine. You should be able to freeze either the baked or unbaked tart — wrap it tightly in foil, then in plastic wrap or a freezer zip-top bag, and then freeze for up to a month. No need to thaw before baking or re-heating. Let us know how it works out!
Hi, ingredients for Trader Joe’s frozen pie crusts include palm oil and butter. The crust is high in total fat (13 grams) and saturated fat (7 grams) and is extremely crumbly even when carefully thawed and unrolled. Be ready to do a lot of surgery patching it together.