Caramelized Onion Tart with Mushrooms

Buttery puff pastry topped with sweet caramelized onions, savory mushrooms, and melted cheese — an elegant, crowd-pleasing appetizer.

This Caramelized Onion Tart with Mushrooms is everything you want in a rustic, savory appetizer. With deeply golden caramelized onions, earthy sautéed mushrooms, and fresh herbs baked on a flaky puff pastry base, it’s simple to make yet irresistibly flavorful. Finished with melted Gruyère and mozzarella, this tart makes an impressive party centerpiece or a cozy vegetarian meal paired with a salad.

Why You’ll Love This

• Impressive, yet easy: No pastry skills needed — store-bought puff pastry makes this elegant tart achievable for everyone.
• Make-ahead friendly: You can prep the mushrooms and onions a day in advance.
• Flavor-packed layers: Caramelized onions, herbs, and two kinds of mushrooms make for deep, rich flavor.
• Versatile: Serve as an appetizer, brunch dish, or vegetarian main.
• Customizable: Easily switch up the cheeses or add other toppings like goat cheese, spinach, or sun-dried tomatoes.

Ingredients

For the Tart

• 4 tablespoons unsalted butter, divided
• 3 medium sweet onions, thinly sliced
• Salt and ground black pepper, to taste
• 1 tablespoon brown sugar
• ¼ cup sherry or dry white wine
• 1 tablespoon Worcestershire sauce
• ¼ cup beef stock (or vegetable stock for vegetarian option)
• 8 oz shiitake mushrooms, thinly sliced
• 8 oz baby bella (cremini) mushrooms, thinly sliced
• 4 cloves garlic, minced
• 1 teaspoon fresh rosemary, finely chopped
• 1 tablespoon fresh thyme leaves, divided
• 1 package (14 oz) puff pastry, thawed
• 1½ cups grated Gruyère cheese
• ½ cup shredded mozzarella cheese
• 1 egg, whisked (for egg wash)

Instructions

Step 1: Caramelize the Onions

1. Heat 2 tbsp of butter in a large skillet over medium heat.
2. Add onions, season with salt, pepper, and brown sugar.
3. Cook for 20–30 minutes, stirring frequently, until soft and golden.
4. Add sherry and Worcestershire sauce; boil 1 minute. Add stock and boil another minute.
5. Transfer onions to a bowl and set aside.

Step 2: Cook the Mushrooms

1. In the same skillet, melt remaining 2 tbsp butter over medium-high heat.
2. Add mushrooms, season with salt and pepper, and sauté for about 7 minutes.
3. Stir in garlic, rosemary, and 1 tsp thyme; cook 1–2 more minutes.
4. Transfer mushrooms to a paper towel-lined bowl to drain excess moisture.

Step 3: Assemble and Bake

1. Preheat oven to 400°F (200°C). Line a baking sheet with parchment.
2. Roll out puff pastry on a floured surface to about ⅛” thick. Score a ½-inch border around the edges. Prick center with a fork. Chill if dough becomes too soft.
3. Sprinkle 1 cup Gruyère over the pastry, then layer caramelized onions and mushrooms. Top with remaining Gruyère and mozzarella.
4. Brush edges with egg wash.
5. Bake for 25–30 minutes or until golden brown.

Step 4: Serve

Let tart cool for 10 minutes, garnish with remaining thyme, slice, and serve warm or at room temperature.

Tips / Storage / FAQs

Tips

• Use both shiitake and cremini mushrooms for balanced texture and flavor.
• Make onions and mushrooms a day ahead and bring to room temp before assembling.
• Don’t skip the egg wash — it helps brown the crust and keeps it from getting soggy.
• Chill the pastry before baking to ensure flakiness.

Storage

• Store leftover tart slices in the refrigerator for up to 3 days. Reheat in the oven at 350°F to keep the crust crisp.
• Not freezer-friendly once baked, but components (onions and mushrooms) can be frozen separately.

FAQs

• Can I use pre-made caramelized onions? Yes, if short on time, store-bought works.
• Can I swap the cheese? Absolutely. Try goat cheese, fontina, or brie.
• Is there a vegan version? Use vegan butter, dairy-free cheese, and a plant-based puff pastry.

Final Thoughts

Whether you’re serving guests or treating yourself, this Caramelized Onion Tart with Mushrooms delivers gourmet flavor with minimal effort. It’s the kind of dish that’s as perfect for cozy nights as it is for impressing at dinner parties. Don’t be surprised if it disappears in minutes — it’s that good!

The Goods

Caramelized Onion Tart with Mushrooms

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Savory and elegant, this Caramelized Onion Tart with Mushrooms features caramelized onions, mushrooms, fresh herbs, and cheese on flaky puff pastry. Perfect as a crowd-pleasing appetizer or vegetarian main dish.

Course Appetizer

Cuisine American

Recipes

For the Tart

• 4 tablespoons unsalted butter divided
• 3 medium sweet onions thinly sliced
• Salt and ground black pepper to taste
• 1 tablespoon brown sugar
• ¼ cup sherry or dry white wine
• 1 tablespoon Worcestershire sauce
• ¼ cup beef stock or vegetable stock for vegetarian option
• 8 oz shiitake mushrooms thinly sliced
• 8 oz baby bella cremini mushrooms, thinly sliced
• 4 cloves garlic minced
• 1 teaspoon fresh rosemary finely chopped
• 1 tablespoon fresh thyme leaves divided
• 1 package 14 oz puff pastry, thawed
• 1½ cups grated Gruyère cheese
• ½ cup shredded mozzarella cheese
• 1 egg whisked (for egg wash)

Instructions

Step 1: Caramelize the Onions

• Heat 2 tbsp of butter in a large skillet over medium heat.
• Add onions, season with salt, pepper, and brown sugar.
• Cook for 20–30 minutes, stirring frequently, until soft and golden.
• Add sherry and Worcestershire sauce; boil 1 minute. Add stock and boil another minute.
• Transfer onions to a bowl and set aside.

Step 2: Cook the Mushrooms

• In the same skillet, melt remaining 2 tbsp butter over medium-high heat.
• Add mushrooms, season with salt and pepper, and sauté for about 7 minutes.
• Stir in garlic, rosemary, and 1 tsp thyme; cook 1–2 more minutes.
• Transfer mushrooms to a paper towel-lined bowl to drain excess moisture.

Step 3: Assemble and Bake

• Preheat oven to 400°F (200°C). Line a baking sheet with parchment.
• Roll out puff pastry on a floured surface to about ⅛” thick. Score a ½-inch border around the edges. Prick center with a fork. Chill if dough becomes too soft.
• Sprinkle 1 cup Gruyère over the pastry, then layer caramelized onions and mushrooms. Top with remaining Gruyère and mozzarella.
• Brush edges with egg wash.
• Bake for 25–30 minutes or until golden brown.

Step 4: Serve

• Let tart cool for 10 minutes, garnish with remaining thyme, slice, and serve warm or at room temperature.

Tips / Storage / FAQs

Tips

• Use both shiitake and cremini mushrooms for balanced texture and flavor.
• Make onions and mushrooms a day ahead and bring to room temp before assembling.
• Don’t skip the egg wash — it helps brown the crust and keeps it from getting soggy.
• Chill the pastry before baking to ensure flakiness.

Storage

• Store leftover tart slices in the refrigerator for up to 3 days. Reheat in the oven at 350°F to keep the crust crisp.
• Not freezer-friendly once baked, but components (onions and mushrooms) can be frozen separately.

Notes

Can I use pre-made caramelized onions? Yes, if short on time, store-bought works.

Can I swap the cheese? Absolutely. Try goat cheese, fontina, or brie.

Is there a vegan version? Use vegan butter, dairy-free cheese, and a plant-based puff pastry.