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Classic French Onion Tart

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A rustic and savory French tart made with caramelized onions and creamy custard nestled in a buttery crust—golden, cheesy, and deeply flavorful with every slice.

Ingredients

Scale
  • 1 1/4 cups all-purpose flour
  • 1/2 cup cold unsalted butter, cubed
  • 1/4 teaspoon salt
  • 3–4 tablespoons cold water
  • 3 large yellow onions, thinly sliced
  • 2 tablespoons olive oil
  • 1 tablespoon unsalted butter
  • 1/2 teaspoon salt
  • 1/4 teaspoon black pepper
  • 1/4 teaspoon dried thyme
  • 3 large eggs
  • 1/2 cup heavy cream
  • 1/2 cup milk
  • 1/2 cup grated Gruyère cheese

Instructions

  1. In a bowl, combine flour and salt. Cut in the butter until mixture resembles coarse crumbs. Add cold water, one tablespoon at a time, until dough comes together. Wrap in plastic and chill for 30 minutes.
  2. Preheat oven to 375°F (190°C). Roll out the chilled dough and fit into a 9-inch tart pan. Trim edges and prick base with a fork.
  3. Blind bake the crust for 10 minutes using parchment and pie weights. Remove weights and bake another 5 minutes. Set aside.
  4. In a large skillet, heat olive oil and butter over medium heat. Add sliced onions and cook slowly, stirring often, for 25–30 minutes until golden and caramelized.
  5. Season with salt, pepper, and thyme. Let cool slightly.
  6. In a bowl, whisk together eggs, cream, and milk. Stir in caramelized onions and Gruyère cheese.
  7. Pour filling into pre-baked crust and smooth top. Bake for 30–35 minutes or until golden brown and just set.
  8. Cool for 10 minutes before slicing. Serve warm or at room temperature.

Notes

  • Caramelizing the onions slowly ensures deep, sweet flavor—don’t rush this step.
  • Blind baking the crust prevents it from getting soggy once the filling is added.
  • Gruyère adds a nutty richness, but Comté or Emmental can be used as substitutes.
  • Serve with a simple green salad for a complete meal.

Nutrition

Keywords: French onion tart, caramelized onion tart, savory tart, Gruyère quiche, French baking, vegetarian tart

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