Upside-Down Onion and Gruyère Tarts

Why You’ll Love This Recipe

I love the elegance of these tarts yet they’re surprisingly simple. The honey (or hot honey) adds a gentle sweetness that balances the buttery, savory Gruyère. With thyme’s herbaceous note and a crispy pastry base, each tartlet feels indulgent, yet unfussy enough for everyday. I can easily make them for brunch, a light dinner, or even an elegant starter.

Ingredients

(Note: All ingredient amounts are listed in the recipe card below.)

1 sheet of puff pastry, thawed
1 yellow onion, thinly sliced
3 tablespoons honey or homemade hot honey, divided
Fresh thyme leaves, salt, and black pepper, to taste
18 pieces thinly sliced gruyere cheese, or as needed
1 egg, beaten

Directions

I begin by preheating my oven as directed on the puff pastry package—typically around 400°F (200°C). I roll out the thawed sheet of puff pastry just slightly to smooth any creases, keeping it on its parchment backing.
In a skillet over medium heat, I sauté the thinly sliced yellow onion until it becomes translucent and golden-brown, coaxing out its sweetness. I stir in two tablespoons of honey (or hot honey, if I’m going for a kick) and allow the onions to lightly caramelize just a minute or two longer then I season with fresh thyme leaves, salt, and black pepper to taste.
I spoon the onions, honey, and thyme mixture onto the puff pastry, spreading it evenly to cover all but about a half-inch border. I lay the Gruyère slices over the onions layering until I use about 18 slices or I’m happy with the coverage. I fold the pastry edges up and over to create a rustic border.
I brush the exposed pastry edges with the beaten egg for a glossy finish. Then I bake the tart in the preheated oven until the pastry is puffed and golden usually 15 to 20 minutes. Once it’s out of the oven, I drizzle the remaining tablespoon of honey over the top for extra shine and sweetness, then let it cool just slightly before slicing.

Servings and Timing

I typically get about 6 to 8 tart servings from one sheet of puff pastry. The prep sautéing onions and assembling the tart takes around 20 minutes. Baking takes about 15 to 20 minutes, so I’m looking at roughly 35 to 40 minutes total from start to finish.

Variations

I sometimes swap Gruyère for other flavorful cheeses like fontina or sharp cheddar if I’m in a pinch I just adjust the amount to taste. Instead of yellow onions, I’ve tried red onions for a sharper, slightly sweeter flavor. For an herbal twist, I experiment with rosemary or tarragon in place of thyme. If I want more texture, I might sprinkle a few toasted walnuts or pine nuts over the onions before adding the cheese. And of course, using hot honey gives a delightful spicy-sweet contrast.

Storage/Reheating

I store leftover slices in an airtight container in the refrigerator for up to 3 days. To reheat, I pop them into a 350°F (175°C) oven for 8 to 10 minutes until the pastry crisps up again. I avoid microwaving, because that makes the pastry soggy for me, the oven is the best way to bring back that flaky crunch.

FAQs

What kind of puff pastry should I use?

I use the frozen, store-bought sheet variety thawed according to package directions before baking. It gives me that classic flaky texture without the fuss of making pastry from scratch.

Can I make these tarts ahead of time?

Yes I assemble the tart, then refrigerate it unbaked. When ready, I brush with egg wash, bake, and drizzle with honey.

What is hot honey, and how can I make it?

Hot honey is honey infused with chili. I make it by warming honey gently with a pinch of red chili flakes for 10–15 minutes, then straining out the flakes. It gives a sweet-heat that’s fantastic with cheese.

Is there a vegetarian version?

Yes this recipe is already vegetarian. The Gruyère is made with microbial (non-animal) rennet at many brands, but I always check the label if strict vegetarian ingredients matter to me.

Can I use a different cheese?

Absolutely I’ve used fontina, smoked mozzarella, or sharp cheddar. Just pick a melty, flavorful cheese and adjust quantity to cover the onions.

How do I know when the onions are properly caramelized?

I look for a deep golden color and a soft, jam-like texture. Letting them cook slowly over medium heat brings out their sweetness without burning.

Can I double the recipe?

Yes I double everything and bake on two sheet pans, or get two tarts from one larger puff pastry sheet if I have it, adjusting bake time as needed until golden.

What’s the best way to cut and serve the tart?

I let it rest a couple minutes after baking, then use a sharp knife or pastry cutter to divide into six to eight wedges. Serving warm keeps the cheese gooey and the crust crisp.

Can I freeze leftovers?

I’ve frozen cooled slices in an airtight container for up to a month. I let them thaw overnight in the fridge, then reheat in a 350 °F oven until crisp and warmed through.

Conclusion

I find these upside-down onion and Gruyère tarts irresistible combining flaky pastry, richly caramelized onions, nutty cheese, and a hint of floral or spicy honey creates a harmony of flavors. Whether I’m serving them as an appetizer, brunch treat, or a cozy dinner with salad, they always get devoured.

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