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An extreme close-up of a savory puff pastry tart, showing the rich texture of the caramelized onions and melted Gruyère cheese.

Caramelized Onion Tart: The Ultimate Guide to a Rich & Savory Pastry

This Caramelized Onion Tart features a buttery puff pastry crust, a rich and jammy onion filling, and nutty Gruyère cheese. An easy, elegant recipe for the perfect sweet and savory tart for any occasion.
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Prep Time 20 minutes
Cook Time 1 hour 10 minutes
Total Time 1 hour 30 minutes
Servings: 8 slices
Course: Appetizer, Dinner, Lunch
Cuisine: French
Calories: 350
Ingredients Equipment Method Notes

Ingredients
  

  • 1.5 tbsp Unsalted Butter
  • 1.5 tbsp Olive Oil
  • 3 Large Yellow Onions thinly sliced
  • 1 tsp Balsamic Vinegar
  • 1 tsp Fresh Thyme Leaves
  • 1/2 tsp Salt
  • 1/4 tsp Black Pepper
  • 1 sheet Puff Pastry thawed
  • 1 cup Gruyère Cheese shredded
  • 1 Large Egg
  • 1/4 cup Heavy Cream

Equipment

  • 1 Large Skillet
  • 1 Baking sheet

Instructions
 

  1. In a large skillet, melt butter with olive oil over medium-low heat. Add sliced onions and salt. Cook, stirring occasionally, for 45-50 minutes until deeply golden and jammy. Stir in balsamic vinegar and thyme; cook for 2 more minutes.
  2. Preheat oven to 400°F (200°C). Place the puff pastry on a parchment-lined baking sheet. Score a ½-inch border around the edges without cutting through. Prick the inside area with a fork.
  3. Sprinkle the shredded Gruyère inside the scored border. Top evenly with the caramelized onions. In a bowl, whisk the egg and heavy cream with a pinch of salt and pepper. Pour the mixture over the onions.
  4. Bake for 20-25 minutes, until the pastry is puffed and golden brown. Let cool slightly before slicing.

Notes

Make Ahead Tip: The onions can be caramelized up to 3 days in advance and stored in the refrigerator.
Storage: Store leftover tart in an airtight container in the refrigerator for up to 3 days. Reheat in the oven or air fryer for best results.
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