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An onion tart. A green napkin, forks, and fresh thyme sprigs are in the background.
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5 from 4 votes

Caramelized Onion Tart

An easy and elegant party appetizer
Prep Time40 minutes
Cook Time30 minutes
Total Time1 hour 10 minutes
Course: Appetizer
Cuisine: American, French
Diet: Lower Carb, Vegetarian
Servings: 8
Calories: 250kcal
Author: Anne Danahy, RD

Equipment

  • 1 10-inch tart pan with removable bottom

Ingredients

  • 2 large sweet onions halved and sliced thin
  • 1 Tablespoon olive oil
  • 4 sprigs fresh thyme divided
  • ½ teaspoon kosher salt
  • ⅛ teaspoon ground pepper
  • 1 premade pie crust
  • 2 large eggs
  • 3 Tbs cream
  • 5 oz Gruyere cheese shredded, 1 ½ cups
US Customary - Metric

Instructions

  • Preheat oven to 375℉. Set the rack to the middle position. Spray a 10-inch tart pan with a removable bottom with cooking spray and set it aside.
  • Cut the onions into thin slices.
  • Heat the olive oil in a large saute pan over medium-high heat. Add the onions, 2 sprigs of fresh thyme, salt, and pepper, and saute for 5 minutes, stirring to coat everything well.
    Add ¼ cup of water to the onions. Cover the pan and cook the onions for 10 minutes or until wilted. Remove the lid and finish cooking the onions until they are completely soft and caramelized, about 20 minutes. Remove the thyme stems.
  • While the onions saute, press the pie crust into a 10-inch tart pan with a removable bottom pressing the crust halfway up the sides. Cover the bottom of the tart crust with parchment paper, and fill it with pie weights.
    Bake tart crust 15-20 minutes, until it starts to turn golden. Remove from oven and let cool a bit. Remove the parchment paper and pie weights when it's cool enough to handle.
  • Reduce oven temperature to 350℉.
  • Shred the cheese and add the remaining thyme leaves to the graded cheese.
  • Whisk the eggs and cream in a small bowl of measuring cup and set aside.
  • Spread grated cheese-thyme mixture evenly over the bottom of the tart crust.
    Spread caramelized onions over the cheese, covering the entire crust.
    Pour the egg-cream mixture evenly over onions. Smooth it with a spatula to ensure the crust is evenly covered.
  • Return the tart to the oven and bake for another 30 minutes at 350℉, until golden brown and the filling is set.
  • Serve warm or at room temperature.

Notes

This is best served the same day but you can store leftovers wrapped in foil in the refrigerator. Reheat in the oven at 325ºF for about 15 minutes. 
 

Nutrition

Calories: 250kcal | Carbohydrates: 17g | Protein: 9g | Fat: 16g | Saturated Fat: 7g | Polyunsaturated Fat: 1g | Monounsaturated Fat: 7g | Trans Fat: 0.01g | Cholesterol: 72mg | Sodium: 385mg | Potassium: 160mg | Fiber: 1g | Sugar: 4g | Vitamin A: 343IU | Vitamin C: 5mg | Calcium: 213mg | Iron: 1mg