Upside Down Onion Tart

Name: Upside Down Onion Tart
Prep time: 20 min
Cook time: 30 min
Total time: 50 min
Yield: 9 to 12 squares
Cuisine: French
Ingredients: 2 small to medium red onions; 2 tablespoons extra virgin olive oil; 4 tablespoons honey; 0.5 teaspoon flaky sea salt, plus extra for serving; 0.5 teaspoon ground black pepper; 6 to 8 sprigs fresh thyme, plus extra leaves for serving; 3 ounces Gruyere cheese, thinly sliced; 1 sheet frozen puff pastry, thawed; 1 large egg, beaten with 1 teaspoon water; Balsamic glaze, optional for serving

This beautiful upside down onion tart features caramelized onions, melted gruyere cheese, and fresh thyme on buttery puff pastry.

By Recipes By Nani· 🌍 French· October 7, 2026

recipesbynani.com

Prep

20 minutes

Cook

30 minutes

Total

50 minutes

Serves

9 to 12 squares

French cooking has a reputation for being complicated, but many of the best dishes come from simple, humble ingredients. When I was traveling through Alsace, I fell in love with onion tart. It is essentially just pastry, onions, cheese, and cream, but the combination is absolutely spectacular and feels so special for any gathering.

My favorite trick for this recipe is the upside down method. By layering your honey, onions, and cheese on the baking sheet before topping them with the puff pastry, you get perfectly caramelized edges without having to cook the onions on the stove for an hour. It is a real time saver that makes you look like a pro.

🧺 Ingredients

2 small to medium red onions
2 tablespoons extra virgin olive oil
4 tablespoons honey
0.5 teaspoon flaky sea salt, plus extra for serving
0.5 teaspoon ground black pepper
6 to 8 sprigs fresh thyme, plus extra leaves for serving
3 ounces Gruyere cheese, thinly sliced
1 sheet frozen puff pastry, thawed
1 large egg, beaten with 1 teaspoon water
Balsamic glaze, optional for serving

👩‍🍳Instructions

1
Preheat your oven to 400 degrees Fahrenheit and line a large rimmed baking sheet with parchment paper.
2
Peel the onions and slice them crosswise into 1/4 inch thick rounds, keeping the rings intact as discs.
3
Create 6 equal patches of olive oil on your parchment paper, arranged in 2 rows of 3.
4
Drizzle the honey over each oil patch, then sprinkle with the salt, pepper, and a sprig of fresh thyme.
5
Place the largest onion discs over the honey patches, then use the smaller slices to fill in any gaps so the pan is mostly covered.
6
Layer the slices of Gruyere cheese directly over the onions.
7
Place the sheet of puff pastry over the top of the onions and cheese, trimming the edges if it is larger than your onion arrangement.
8
Tuck the edges of the pastry down around the onions and brush the top lightly with the egg wash.
9
Bake for 20 to 25 minutes until the pastry is puffed and deep golden brown.
10
Let the tart cool for 5 minutes, then carefully place a large cutting board over the tray and flip the tart over to reveal the caramelized onions.
11
Sprinkle with fresh thyme and a little extra flaky salt before serving, adding a drizzle of balsamic glaze if you like.

💡 Tips

Serve this tart warm as an appetizer or a light lunch. If you have leftovers, store them in an airtight container in the fridge and reheat in a 350 degree oven for a few minutes to get the pastry crisp again.

#Vegetarian #Appetizer #French #Easy Recipe

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