French Onion Tart

With a generous layer of caramelized onions and plenty of sharp Gruyère cheese, this party-ready tart packs the rich depth of French onion soup into every bite.

Original recipe source

Cook time: 45 minutes

Servings: 4

Ingredients

• 1.5 lb onions preferably yellow, halved, thinly sliced
• 3 Tbsp unsalted butter
• 0.75 tsp kosher salt Diamond Crystal or 0.5 tsp. Morton
• 0.5 cup water for adding in splashes
• 1 clove garlic finely chopped
• 2 tsp sherry vinegar or red wine vinegar
• 2 tsp Worcestershire sauce
• 1 tsp freshly ground pepper
• 2 oz Gruyère coarsely grated
• 14 oz frozen puff pastry one 14-oz. package or half of a 17.3-oz. package, thawed
• 0 parchment paper
• 1 Tbsp Dijon mustard
• 2 oz Gruyère remaining, coarsely grated
• 0 chives chopped, for serving

Instructions

1. Place a rack in lower third of oven; preheat to 400°F.
2. Combine onions, butter, and salt in a large Dutch oven over medium heat, cover, and cook, stirring occasionally until onions are softened and translucent, 9-11 minutes. Uncover and continue to cook, adding splashes of water and stirring until deep golden brown, 15-20 minutes.
3. Remove pot from heat and stir in garlic, vinegar, Worcestershire sauce, pepper, and 2 oz. Gruyère into onion mixture.
4. If using a 14-oz. puff pastry package, cut dough in half and roll 1 half into a 10x8" rectangle on parchment paper. If using a 17.3-oz. package, roll out 1 sheet to smooth out creases.
5. Lightly score a 1/2" border around the pastry edges, prick in a few spots with a fork, then bake until puffed and golden, 15-18 minutes. Flatten center slightly.
6. Spread Dijon mustard over pastry within the border, then add onion mixture evenly on top and scatter remaining Gruyère over.
7. Bake tart until the pastry is golden brown and cheese is melted, 10-15 minutes. Let cool 5 minutes, then cut into squares and top with chopped chives.