Go Back
A golden-brown onion tart with caramelized onions on top.

Double-Layered Caramelized Onion Tart

This impressive double-layered caramelized onion tart features a tender, flaky crust filled with a sweet and savory caramelized onion base and a rich, creamy egg custard. Perfect for an appetizer, brunch, or light meal.
Print Recipe Pin Recipe
Prep Time 45 minutes
Cook Time 1 hour 30 minutes
Total Time 2 hours 15 minutes
Servings: 8 slices
Calories: 450
Ingredients Equipment Method Notes

Ingredients
  

For the Pastry
  • 1 ½ cups all-purpose flour
  • ½ teaspoon salt for pastry
  • ½ cup unsalted butter very cold and cut into small pieces
  • ¼ cup ice water or a little more, as needed
For the Caramelized Onions
  • 4 large yellow onions about 3 lbs, thinly sliced
  • 2 tablespoons olive oil
  • 1 tablespoon unsalted butter for onions
  • ½ teaspoon salt for onions, plus more to taste
  • ¼ teaspoon black pepper for onions, plus more to taste
For the Custard
  • 2 large eggs
  • 1 cup heavy cream
  • ½ cup whole milk
  • ¼ cup grated Gruyere cheese optional, but highly recommended
  • nutmeg Pinch of

Equipment

  • large bowl
  • pastry blender
  • large heavy-bottomed skillet or Dutch oven
  • 9-inch tart pan with a removable bottom
  • parchment paper
  • pie weights or dried beans
  • medium bowl
  • wire rack

Method
 

Prepare the Pastry
  1. Combine flour and salt in a bowl, then cut in cold butter until crumbly. Add ice water gradually to form a dough; refrigerate for 30 minutes.
Caramelize the Onions
  1. Heat oil and butter in a skillet, then add sliced onions, salt, and pepper. Cook slowly for 30-45 minutes until deeply golden and soft, then cool slightly.
Pre-bake the Crust (Blind Bake)
  1. Preheat oven to 375°F (190°C). Roll out chilled dough, fit into a 9-inch tart pan, and trim edges. Blind bake for 15 minutes with pie weights, then remove weights and bake for another 5-7 minutes until lightly golden.
Prepare the Custard
  1. While the crust bakes, whisk together eggs, heavy cream, milk, Gruyere (if using), nutmeg, and seasoning in a medium bowl.
Assemble the Tart
  1. Spread half the caramelized onions in the pre-baked crust, pour half the custard over, then add the remaining onions and custard, gently wiggling to fill gaps.
Bake the Tart
  1. Reduce oven to 350°F (175°C) and bake for 35-45 minutes, until the center is set and the top is golden brown.
Cool and Serve
  1. Cool the tart on a wire rack for at least 15-20 minutes before slicing and serving to allow the custard to fully set.

Notes

For best results, ensure your butter and ice water are very cold when making the pastry. Caramelizing the onions slowly enhances their flavor significantly. If your crust edges are browning too quickly during blind baking, you can cover them with foil.