Caramelized Onion & Gruyère Tartlets
Buttery puff pastry filled with slowly caramelized onions, nutty Gruyère and fresh thyme. These little tartlets are simple, savoury and perfect for entertaining.
Prep time
15 min
Cook time
45–50 min
Serves
Ingredients
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- 1 sheetfrozen puff pastry, thawed but still cold
- 2 largeyellow onions, thinly sliced
- 1 tbspbutter
- 1 tbspolive oil
- ½ tspfine sea salt
- ¼ tspfreshly ground black pepper
- 1 tspfresh thyme leaves, plus more for finishing
- 1 tspDijon mustard
- 1 cupfreshly grated Gruyère cheese
- 1 largeegg
- 1 tspwater
Ingredients
- 1 sheetfrozen puff pastry, thawed but still cold
- 2 largeyellow onions, thinly sliced
- 1 tbspbutter
- 1 tbspolive oil
- ½ tspfine sea salt
- ¼ tspfreshly ground black pepper
- 1 tspfresh thyme leaves, plus more for finishing
- 1 tspDijon mustard
- 1 cupfreshly grated Gruyère cheese
- 1 largeegg
- 1 tspwater
Instructions
- 1
Heat the butter and olive oil in a large skillet over medium-low heat.
- 2
Add the sliced onions and salt. Cook slowly for 30–35 minutes, stirring occasionally, until the onions are very soft and a deep golden brown. If they begin sticking or browning too quickly, add a tablespoon or two of water and continue cooking.
- 3
Stir in the black pepper, thyme and Dijon mustard. Cook for another minute, then remove from the heat and allow the onion mixture to cool.
- 4
Preheat the oven to 400°F (200°C). Lightly grease a 24-cup mini muffin pan.
- 5
Place the cold puff pastry on a lightly floured counter. Gently roll it just enough to smooth the seams and create an even rectangle.
- 6
Cut the pastry into 24 small squares. Gently press one square into each mini muffin cup, allowing the corners to come slightly above the edges.
- 7
Whisk together the egg and water.
- 8
Place approximately 1½ teaspoons of caramelized onion into each pastry cup. Don't overfill them — you want room for the pastry to puff.
- 9
Top each tartlet with a generous pinch of grated Gruyère.
- 10
Lightly brush the exposed pastry edges with the egg wash.
- 11
Bake for 15–18 minutes, until the puff pastry is crisp and deeply golden and the Gruyère is melted and bubbling.
- 12
Let the tartlets rest in the pan for about 5 minutes before carefully removing them.
- 13
Finish with a few fresh thyme leaves and a little freshly ground black pepper. Serve warm or at room temperature.
Melissa's Notes
Give the onions time to caramelize slowly rather than simply brown. Keeping the heat around medium-low allows them to soften and develop their natural sweetness without burning. Thirty minutes or more is quite normal for properly caramelized onions.
Also, let the onions cool before putting them onto the cold puff pastry. Keeping puff pastry relatively cold before it goes into the oven helps give you those flaky layers.
Make Ahead: The caramelized onion mixture can easily be made 1–2 days ahead and refrigerated. You can also assemble the tartlets ahead and refrigerate them until you're ready to bake. For longer storage, assembled puff-pastry onion bites can be frozen and baked later.
Nutrition Information
Per tartlet — based on 12 tartlets
Nutrition information is an estimate and may vary depending on the ingredients and brands used.
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