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French Onion Mushroom Tart

A savory tart with caramelized onions, sautéed mushrooms, and Gruyère cheese on buttery puff pastry.
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Prep Time 35 minutes
Cook Time 25 minutes
Total Time 1 hour
Servings: 6 slices
Course: Lunch, Snack
Cuisine: European, French
Calories: 320

Ingredients
  

Puff Pastry Base
  • 1 sheet puff pastry thawed
  • 1 egg beaten, for egg wash
Caramelized Onions
  • 3 yellow onions thinly sliced
  • 2 tbsp unsalted butter
  • 1 tbsp olive oil
  • 1 tsp sugar
  • to taste salt and pepper
Mushroom Mixture
  • 2 cups cremini mushrooms sliced
  • 1 tbsp olive oil
  • 1 tsp fresh thyme leaves
  • to taste salt and pepper
Cheese and Flavoring
  • 1 cup Gruyère cheese grated
  • 1 tsp balsamic vinegar
  • fresh thyme for garnish

Equipment

  • Mixing bowls
  • Skillet
  • Baking sheet
  • Wire rack

Method
 

  1. In a large skillet over medium heat, melt butter with olive oil. Add onions, sugar, salt, and pepper. Cook until golden brown and caramelized, about 25–30 minutes.
  2. In another skillet, heat olive oil over medium heat. Add mushrooms and thyme, season with salt and pepper, and cook until tender, about 7–10 minutes.
  3. Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
  4. Roll out puff pastry on a lightly floured surface. Transfer to baking sheet. Score a 1-inch border, brush edges with beaten egg.
  5. Spread caramelized onions inside border. Layer mushrooms on top, sprinkle Gruyère cheese, and drizzle balsamic vinegar.
  6. Bake 20–25 minutes until puff pastry is golden and cheese is melted.
  7. Garnish with fresh thyme, slice, and serve warm.

Notes

Make sure to cook onions slowly for best flavor. Puff pastry can be store-bought or homemade.