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French Onion Mushroom Tart

A savory French-style tart made with caramelized onions, golden mushrooms, flaky puff pastry, and rich Gruyère custard.
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Prep Time 25 minutes
Cook Time 35 minutes
Total Time 1 hour
Servings: 6 slices
Course: Appetizer, Main
Cuisine: French, Vegetarian
Calories: 340
Ingredients Equipment Method Notes

Ingredients
  

Base
  • 1 sheet puff pastry thawed
  • 1 tbsp olive oil
  • 1 tbsp butter
Onion Layer
  • 3 yellow onions thinly sliced
  • 2 tbsp butter
  • 1 tsp sugar
  • 0.5 tsp salt
Mushroom Layer
  • 12 oz mushrooms sliced
  • 2 cloves garlic minced
  • 1 tsp thyme fresh or dried
  • 0.5 tsp black pepper
Custard
  • 2 eggs large
  • 0.75 cup heavy cream
  • 0.5 cup Gruyère cheese grated
  • 0.25 cup Parmesan cheese grated

Equipment

  • Skillet
  • Mixing bowl
  • Baking sheet

Method
 

  1. Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
  2. Prepare puff pastry and chill while making fillings.
  3. Caramelize onions slowly in butter until golden.
  4. Sauté mushrooms until browned, then add garlic and thyme.
  5. Whisk eggs, cream, and cheeses together.
  6. Assemble tart layers and pour custard on top.
  7. Bake 30–35 minutes until golden and set.

Notes

Serve warm or room temperature. Excellent for entertaining and make-ahead meals.