Caramelized Onion Tart with Gruyere

Ingredients

• Puff pastry (1 sheet, thawed)
• Onions (3 large, thinly sliced)
• Unsalted butter (2 tablespoons)
• Salt (1/2 teaspoon, plus more for seasoning)
• Black pepper (1/4 teaspoon, plus more for seasoning)
• Sugar (1 teaspoon)
• Fresh thyme (1 tablespoon, chopped)
• Gruyere cheese (1 cup, grated)
• Heavy cream (1/2 cup)
• Eggs (2 large)

Instructions

1. Preheat your oven to 400°F (200°C).
2. In a large skillet, melt the butter over medium heat. Add the sliced onions, salt, black pepper, and sugar.
3. Cook the onions, stirring occasionally, for about 20 minutes, or until they are deeply caramelized and golden brown. This slow cooking brings out their natural sweetness.
4. While the onions are cooking, roll out the puff pastry sheet on a lightly floured surface. Fit the pastry into a 9-inch tart pan, trimming any excess pastry hanging over the edges.
5. In a medium bowl, whisk together the eggs and heavy cream. Season the mixture with a pinch of salt and black pepper.
6. Spread the caramelized onions evenly over the puff pastry base, ensuring they are well-distributed.
7. Pour the egg and cream mixture over the onions, ensuring they are evenly coated and the mixture seeps through.
8. Sprinkle the grated Gruyere cheese and chopped thyme over the top of the tart, adding a lovely herbaceous note.
9. Bake in the preheated oven for 20-25 minutes, or until the tart is golden brown and the filling is set.
10. Allow the tart to cool slightly before slicing. Serve warm or at room temperature for a delightful experience.