Caramelized Onion and Gruyère Tart
Deeply caramelized onions and nutty gruyère in a buttery tart shell - rich and savory
Ingredients
- 1 sheetpuff pastry(thawed)
- 4 largeyellow onions(thinly sliced)
- 4 tbspunsalted butter
- 1 tbspfresh thyme leaves
- 1 tspkosher salt
- 0.5 tspblack pepper
- 1 tbspbalsamic vinegar
- 6 ozgruyère cheese(grated)
- 1egg(beaten for wash)
📝 Make Ahead
Caramelize onions up to 3 days ahead and refrigerate. Assemble and bake day of serving.
Instructions
- Melt butter in large skillet over medium-low heat
- Add onions and salt, stirring to coat
- Cook slowly, stirring occasionally, until deeply golden and jammy, 45-60 minutes
- Add balsamic vinegar and thyme in last 5 minutes, stir to combine
- Let onions cool slightly
- Preheat oven to 400°F and line baking sheet with parchment
- Unroll puff pastry onto baking sheet
- Score a 1-inch border around edges with knife tip - do not cut through
- Spread onions within border, leaving edges bare
- Top evenly with grated gruyère
- Brush exposed border with egg wash
- Bake 20-25 minutes until pastry is deeply golden and cheese is bubbling
- Cool 10 minutes, then cut into squares or strips
💡 Pro Tips
True caramelized onions take at least 45 minutes - don't rush. Low and slow is essential. The onions should be deep amber, not just softened. Gruyère melts beautifully; aged Swiss is an acceptable substitute. The balsamic adds depth but shouldn't dominate. Serve warm or at room temperature.
📜 History
This tart draws from the French tradition of pissaladière, the onion-topped flatbread of Provence. Slow-cooked onions develop complex sweetness through the Maillard reaction, while gruyère adds Alpine nuttiness. The combination epitomizes fall's transition to richer, more substantial fare.