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Katherine Peterson

Savory Roasted Garlic Onion Tart

This caramelized onion tart features flaky puff pastry topped with slowly caramelized yellow onions, roasted garlic, melted Gruyère cheese, and fresh thyme. The crisp golden crust and rich, savory topping make it an excellent appetizer or side dish for holiday meals and gatherings. Prepare the onions and roasted garlic ahead to simplify assembly and enjoy the tart warm after baking.
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Prep Time 10 minutes
Cook Time 1 hour 30 minutes
Total Time 1 hour 40 minutes
Servings: 8
Course: Appetizer
Cuisine: American, French
Ingredients Equipment Method Notes

Ingredients
  

  • 1 tablespoon olive oil
  • 3 tablespoons butter
  • 2 large yellow onions thinly sliced
  • 1 head garlic with the top trimmed off
  • 1 sheet puff pastry thawed in the refrigerator overnight
  • 1¾ cups shredded Gruyère cheese
  • 2 sprigs fresh thyme leaves removed from the stems
  • A pinch of salt for seasoning the onions
  • A little extra olive oil for drizzling over the garlic
  • Milk or egg wash for brushing the pastry edges
  • A little flour for dusting the work surface

Equipment

  • Large cast-iron skillet or Dutch oven
  • Baking sheet
  • Parchment paper
  • Aluminum foil (or parchment paper for roasting the garlic)
  • Rolling Pin
  • sharp knife
  • Cutting board
  • Fork
  • Pastry brush
  • Measuring spoons
  • Cheese grater (if using a block of Gruyère)
  • Spatula or spoon

Method
 

  1. Caramelize the Onions: Heat the olive oil and butter in a large cast-iron skillet or Dutch oven over medium heat.
    Once hot, add the thinly sliced onions and cook for 5 minutes, stirring occasionally.
    Reduce the heat to low, add a pinch of salt, and continue cooking for 45 minutes to 1 hour, stirring occasionally, until the onions are deeply caramelized.
    Remove from the heat and allow them to cool completely, ideally overnight.
  2. Roast the Garlic: Preheat the oven to 400°F. Drizzle the trimmed head of garlic with a little olive oil and wrap it in aluminum foil or parchment paper.
    Bake for 40–45 minutes, until the garlic has softened.
    Allow it to cool, then squeeze the cloves out of their skins and set aside.
  3. Prepare the Baking Sheet: Line a baking sheet with parchment paper and set it aside.
  4. Roll Out the Puff Pastry: Lightly flour a clean work surface.
    Roll the thawed puff pastry into a large rectangle measuring approximately 10 × 16 inches.
    Carefully transfer the pastry to the prepared baking sheet.
  5. Shape the Tart Base: Using a knife, lightly score a border about 1 inch from the edges of the pastry, taking care not to cut all the way through.
    Prick the pastry inside the border all over with a fork to help prevent excessive bubbling during baking.
  6. Preheat the Oven: Set the oven temperature to 375°F in preparation for baking the assembled tart.
  7. Add the Gruyère Cheese: Sprinkle the shredded Gruyère evenly over the center of the puff pastry, keeping the scored border clear.
  8. Add the Garlic, Onions, and Thyme: Distribute the roasted garlic cloves over the cheese.
    Arrange the cooled caramelized onions on top, then sprinkle with the fresh thyme leaves.
  9. Brush the Pastry Edges: Lightly brush the exposed pastry border with milk or egg wash to encourage a golden finish.
  10. Bake the Tart: Bake at 375°F for 20 minutes. Increase the oven temperature to 400°F and continue baking for another 6–8 minutes, until the pastry edges are puffed, browned, and crisp.
  11. Cool and Serve: Remove the tart from the oven and allow it to cool slightly before slicing. Serve warm.

Notes

  • Prepare Ahead: Caramelize the onions and roast the garlic in advance. Allow both to cool completely, ideally overnight, before assembling the tart.
  • Thaw the Pastry Properly: Thaw the puff pastry in the refrigerator overnight so it is ready to roll out.
  • Caramelize Slowly: Cook the onions over low heat for 45 minutes to 1 hour after the initial 5 minutes of cooking. Stir occasionally until they become deeply caramelized.
  • Choose Good Gruyère: Shred the Gruyère cheese before assembling the tart to help distribute it evenly across the pastry.
  • Prevent Excessive Puffing: Score a 1-inch border around the pastry without cutting all the way through, then prick the center with a fork.
  • Watch the Final Bake: After the initial 20 minutes at 375°F, increase the oven temperature to 400°F and bake for another 6–8 minutes, until the edges are browned, puffed, and crisp.
  • Allow a Brief Rest: Let the tart cool slightly before slicing to make serving easier.
  • Storage: The original recipe does not specify storage or reheating times, so follow appropriate food-storage guidance for any leftovers.