Caramelized Onion & Gruyère Tart: Elegant, Savory & Perfectly Buttery

This Caramelized Onion & Gruyère Tart is rich, buttery, and overflowing with deep, savory flavor. Slow-cooked caramelized onions melt into a layer of sharp Gruyère cheese on top of flaky puff pastry. It’s an impressive yet easy, tried-and-tested recipe perfect for brunch, appetizers, or a cozy dinner with a salad on the side.

📋 Ingredients

1 sheet puff pastry, thawed
2 large onions, thinly sliced
2 tablespoons butter
1 tablespoon olive oil
½ teaspoon salt
¼ teaspoon black pepper
1 teaspoon fresh thyme (or ½ teaspoon dried)
1 tablespoon balsamic vinegar (optional, for depth)
1 cup shredded Gruyère cheese
1 egg (for egg wash)

🥧 Instructions

Preheat oven to 400°F (200°C). Heat butter and olive oil in a skillet over medium heat. Add onions, salt, pepper, and thyme. Cook slowly for 20–25 minutes, stirring often, until onions are golden and caramelized. Add balsamic vinegar and cook 1 minute more.
On a baking sheet, unfold the puff pastry. Score a 1-inch border around the edges with a knife (don’t cut through). Brush edges lightly with beaten egg.
Spread caramelized onions evenly inside the border and sprinkle Gruyère on top.
Bake 20–25 minutes until pastry is puffed and golden and cheese is melted. Slice and serve warm.

💡 Tips

Cook onions low and slow for the sweetest flavor. Add a handful of cooked mushrooms for an extra savory twist. Use Gruyère for best melt and flavor, but Swiss cheese also works.