Onion Tart Recipe with Caramelized Onion and Cheese

Are you a fan of French onion soup and savory tarts? If so, then you'll absolutely love this onion tart: a rustic crust filled with creamy, gently sweet caramelized onions, and topped with abundant melted strong cheese.

Why I ❤️ it • Recipe • Ingredients • Preparation

Onion tart.

Why I ❤️ it

Let's share a slice of this marvelous onion tart made with caramelized onions and with a cheese crust. If you love French onion soup, you'll love this rustic, easy-to-make tart.

The result is a crispy crust filled with a creamy, gentle onion filling, with the sweet flavors of slow, gentle caramelization, topped with the contrasting taste of sharp cheeses. This is a new favorite in your tart recipe list, perfect for your dinner party or brunch.

Utensils and tools

• Mixing bowl
  Food processor
• Plastic film
• 12-inch skillet with lid [25 centimeters]
• 10-inch tart pan [20 centimeters]
• Parchment paper
• Pie weights (or dry beans, or any dry pulses)

Ingredients

For the crust

• 1¾ cup whole-wheat flour
• ¾ teaspoon salt
• 1 teaspoon baking soda
• ⅓ cup unsalted butter (melted)
• 1 egg
• ½ cup cold water (may not need all)

For the filling

• ¼ cup olive oil
• 3 pounds of white onion, [1.4 kilogram], halved and sliced thinly
• ½ teaspoon of fresh thyme leaves (or dry if you don't have fresh)
• ½ cup of cooking sherry
• 1 tablespoon garlic salt, (see notes)
• 1 teaspoon black pepper (freshly-cracked, or ground)
• ½ teaspoon nutmeg (freshly grated)
• 2 tablespoons all-purpose flour
• 1 cup of grated Gruyère cheese
• ½ cup shredded sharp cheddar

Preparation

Before starting, please make sure you have all the ingredients and utensils ready.

For the crust

Step 1

In a mixing bowl, mix flour, salt, and baking soda. Pour the mix into the food processor.

Pour in melted butter and egg, and pulse to incorporate. Midway stop and scrape the sides with a spatula moving the flour from the sides to the middle. If the dough is too dry, add cold water by the tablespoon until the dough just forms a ball but is not soggy or sticky.

Step 2

Pour onto the counter and knead the dough lightly until it is smooth (about 1 minute).

Wrap in plastic film and let it rest at room temperature for at least 10 minutes.

For the filling

Step 1

Heat the oil over medium-low heat in the skillet. Add the onions and thyme and stir until the onions are coated with oil. Cover and simmer over for 5 minutes, stirring often.

Step 2

Add the sherry, and simmer until the sherry has mostly evaporated. Cover and simmer over low heat for another 25-30 minutes, or until the onions have turned caramel brown and are very tender.

Season with garlic salt, pepper, and nutmeg.

Step 3

Increase heat to medium-high heat and add flour, sprinkling, and mixing until all the onions are lightly coated with flour. Remove from the heat.

Let it rest until the onion mixture has cooled to room temperature.

To assemble

Step 1

Heat oven to 350 ºF [175 ºC].

Step 2

Roll out the dough with a rolling pin until you have a circle big enough to cover the bottom and sides of the tart pan.

Cover the tart pan with the dough and tidy up the sides using any excess dough. Poke a few holes in the bottom with a fork. Line the bottom with a circle of parchment paper, and place the pie weights or dry beans on the parchment paper.

Step 3

Bake the pie crust in the preheated oven for 15 minutes. Remove from the oven.

Fill the pie crust with the onion mixture, and top with the cheeses.

Step 4

Return to the oven and bake until the cheese is bubbly and golden brown.

Remove from the oven and serve hot.

Top tips

• If you don't have garlic salt, mix ½ tablespoon of regular with ½ tablespoon of garlic powder.
• Whole wheat dough is very fragile and not elastic like regular dough; I've found that the best way to spread it is between two plastic film pieces. There's going to be some patching too. Don't worry too much; that's why I called it "rustic."

Variations

You can make this French onion soup-inspired onion tart with puff pastry for a different and entirely marvelous variation. Instead of making the crust as directed, revert the order of the ingredientes by placing the onions in the pan, followed by the cheese, and topped with a circle of puff pastry, which you'll then bake until the puff pastry is baked.

For a vegan or vegetarian onion tart version, use your favorite cheese substitute (I've found some pretty good vegan ones), or skip the cheese entirely. The onion is sublime in itself. Use your preferred butter substitute for the crust. I have done it with vegetable oil too.

Serving suggestions

This onion tart goes great with your favorite green salad if you serve it for dinner or brunch.

Nutritional information

Calories: 567kcal - Carbohydrates: 50g - Protein: 17g - Fat: 33g - Saturated Fat: 9g - Cholesterol: 36mg - Sodium: 1788mg - Potassium: 526mg - Fiber: 8g - Sugar: 11g - Vitamin A: 335IU - Vitamin C: 16.7mg - Calcium: 379mg - Iron: 2.1mg

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