Caramelized Onion and Gruyere Puff Pastry Tart Tips, FAQ & printable recipe

Tips for success

For the best texture, serve the tart warm, within 30 minutes of baking. The pastry is at its crispiest right out of the oven, and the cheese is beautifully molten.

If you need to hold it longer, keep it in a warm oven (200°F) for up to 30 minutes, but the pastry may soften slightly. To re-crisp, place slices back on a baking sheet and heat at 350°F for 5 minutes.

This tart is endlessly adaptable. Try adding a thin layer of Dijon mustard under the onions for extra tang, or sprinkle with a few chopped walnuts for crunch.

For a vegetarian main, serve with a side salad dressed with lemon vinaigrette. The tart also works well with other cheeses like goat cheese or blue cheese, and you can swap the onions for caramelized fennel or leeks.

Variations

• Mushroom and Thyme: Sauté 8 oz sliced mushrooms with garlic and thyme, then spread over the pastry instead of onions. Top with gruyere and bake as directed. Finish with fresh thyme and a drizzle of truffle oil for extra luxury.
• Apple and Blue Cheese: Thinly slice one apple and toss with a teaspoon of lemon juice. Spread a thin layer of Dijon mustard on the pastry, then layer apples and crumbled blue cheese. Bake until golden, then drizzle with honey and sprinkle with walnuts.
• Tomato and Pesto: Spread a layer of basil pesto on the pastry, then top with sliced cherry tomatoes and shredded mozzarella. Bake until the pastry is golden and the cheese is melted. Garnish with fresh basil leaves and a pinch of red pepper flakes.
• Caramelized Leek and Comte: Replace the onions with caramelized leeks (2 large leeks, sliced and cooked until soft). Use Comte or Swiss cheese instead of gruyere. Finish with a sprinkle of fresh chives and a drizzle of balsamic glaze.

Storage and make-ahead

Fridge

Store leftover tart in an airtight container in the refrigerator for up to 3 days.

Freezer

Freeze baked tart slices in a single layer, then transfer to a freezer bag for up to 2 months. Reheat from frozen in a 350°F oven for 10 minutes.

Reheat

Reheat slices in a 350°F oven for 5-7 minutes until hot and crisp. Avoid microwaving.

Store leftover tart in an airtight container in the refrigerator for up to 3 days. To reheat, place slices on a baking sheet and warm in a 350°F oven for 5-7 minutes, or until heated through and crisp. Avoid microwaving, as it will make the pastry soggy.

The balsamic-caramelized onions can be made up to 1 week ahead and stored in the refrigerator. You can also assemble the entire tart (without baking) up to 24 hours in advance, cover it, and refrigerate.

When ready to bake, add a few extra minutes to the baking time if starting from cold. The baked tart is best served fresh, but leftovers can be reheated.

Serving ideas

Serve this tart as an elegant appetizer at your next dinner party, cut into small squares or rectangles.

It pairs beautifully with a crisp green salad dressed with a simple vinaigrette, or with a glass of dry white wine like Sauvignon Blanc. The tart is also delicious alongside a bowl of tomato soup for a comforting lunch.

For a more substantial meal, serve larger slices with a side of roasted vegetables or a charcuterie board. The tart is versatile enough to be the star of a brunch spread, a picnic, or a holiday gathering. Garnish with extra fresh thyme and a drizzle of balsamic glaze just before serving to make it look even more polished.

Frequently asked questions

Recipe card

Caramelized Onion and Gruyere Puff Pastry Tart

Prep 15 minCook 18 minTotal 33 minServes 6

Ingredients

• 1 sheet puff pastry, thawed (about 10 oz)
• 300 g balsamic-caramelized onions (about 2 cups)
• 1 1/2 cups grated gruyere cheese (about 6 oz)
• 1 tbsp fresh lemon thyme leaves
• 2 tbsp aged balsamic glaze

Instructions

1. Heat the oven to 415°F (215°C). Line a baking sheet with parchment paper. On a lightly floured surface, roll the puff pastry into a 10x14-inch rectangle. Transfer to the prepared sheet and prick all over with a fork. Score a 1-inch border around the edge, being careful not to cut through. Spread the balsamic-caramelized onions evenly over the pastry, staying inside the border. Sprinkle the grated gruyere over the onions.
2. Bake the tart for 18 minutes, until the pastry is puffed and golden brown and the cheese is bubbling and blistered in spots. Rotate the baking sheet halfway through for even browning. The edges should be deeply golden and crisp.
3. Remove the tart from the oven and immediately scatter the fresh lemon thyme leaves over the hot surface. Drizzle with the aged balsamic glaze. Let the tart cool for 5 minutes, then slice into squares or rectangles with a sharp knife. Serve warm.

Contains: gluten, milk

Estimated nutrition per serving

Calories

320

Protein

9 g

Carbohydrates

28 g

Fat

19 g

Automatic estimate from the ingredient list, not laboratory-verified.