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Apple and Caramelized Onion Tart on a wooden board.
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Apple and Caramelized Onion Tart

A recipe for an Apple and Caramelized Onion Tart! This tart has a buttery, flaky crust filled with caramelized onions, Alpine cheese, a savory custard, and thinly sliced apples.
Course Side Dish
Cuisine N/A
Keyword apple, apple pie, caramelized onion, cheese, fall, onion, pie, tart
Prep Time 20 minutes
Cook Time 1 hour 10 minutes
Resting Time: 1 hour
Total Time 2 hours 30 minutes
Servings 1 Tart

Ingredients

Crust:

  • 1 1/2 cups (190 grams) all-purpose flour
  • 1 tablespoon (12 grams) granulated sugar
  • 1/2 teaspoon salt
  • 6 tablespoons (85 grams) unsalted butter chilled and diced, plus more for greasing
  • 1/3 cup (80 milliliters) cold water

Caramelized Onions:

  • 2 tablespoons (28 grams) unsalted butter
  • 1 tablespoon (15 milliliters) olive oil
  • 3 large onions peeled, cut in half, and thinly sliced
  • 1 sprig fresh thyme
  • salt and freshly ground black pepper to taste

Assembling the Tart:

  • 3 ounces (85 grams) Alpine cheese such as Gruyère or Emmentaler, shredded
  • 1/2 tablespoon all-purpose flour
  • 2 large eggs
  • 1/4 cup (60 milliliters) heavy cream
  • 1/4 teaspoon salt
  • pinch freshly ground black pepper
  • pinch freshly grated nutmeg
  • 2 apples cored and thinly sliced
  • 1 tablespoon (14 grams) unsalted butter melted
  • coarse sugar for sprinkling, optional

Instructions

To make the crust:

  • In a large bowl, combine the flour, sugar, and salt.
  • Quickly cut in the cold butter using a dough blender, two forks, or your fingers until blended and no pieces are larger than a pea and the dough has a crumbly texture.
  • Slowly add the cold water to form a soft and smooth dough.
  • Form the dough into a disc, wrap in plastic, and refrigerate until chilled, 30 minutes to 1 hour or up to two days.

To make the caramelized onions:

  • In a wide pot or saucepan, melt together the 2 tablespoons (28 grams) butter and olive oil over medium heat.
  • Once the butter is melted, add the onions and cook, stirring occasionally, until deeply golden and caramelized, about 30 minutes. Adjust heat between medium and low as needed to caramelize the onions without burning.
  • Season with the leaves from the thyme sprig, salt, and freshly ground black pepper.
  • Remove from heat, transfer the caramelized onions to a bowl, and allow to cool to room temperature.

To assemble:

  • Grease a 14 x 4.75 inch (36 x 12 centimeter) rectangular tart pan or 9 inch (23 centimeter) round tart pan with removable base with butter.
  • Remove the chilled dough from the refrigerator and roll on a floured surface into a thin sheet large enough to completely cover the bottom and sides of the pan, about 1/8 inch (3 millimeters) thick.
  • Carefully transfer the sheet to the prepared pan, gently pressing down along the bottom and sides to make sure it is completely covered without any air bubbles. Cut away any excess scraps.
  • Prick across the bottom of the tart with a fork, then place the pan in the refrigerator to chill while the oven preheats.
  • Preheat oven to 400˚F (200˚C).
  • Once preheated, remove the pan from the refrigerator and place on a rimmed baking sheet (to protect the oven just in case any butter seeps through the bottom or anything bubbles over).
  • Cover the crust lightly with a sheet of parchment and fill with ceramic pie weights or uncooked rice. Bake in the preheated oven until starting to set, 10-15 minutes.
  • Carefully remove the parchment sheet with the weights from the crust and allow the crust to cool slightly.
  • In a small bowl, toss the shredded cheese with the flour until evenly coated.
  • Sprinkle the coated cheese across the bottom of the partially baked crust.
  • Cover the cheese with an even layer of the caramelized onions.
  • In a medium bowl, whisk together the eggs, heavy cream, salt, pepper, and nutmeg until evenly blended.
  • Pour the mixture into the tart pan in an even layer over the caramelized onions.
  • Arrange the thin apple slices slightly overlapping across the top of the tart.
  • Gently brush the top of the apple slices with melted butter and, if desired, sprinkle with coarse sugar.
  • Bake in the 400˚F (200˚C) oven until the egg mixture is puffed and the apple slices are lightly golden, about 25-30 minutes.
  • Allow the ingredients to settle in the tart for 5 minutes before carefully removing from the pan.
  • Serve warm or at room temperature.