Upside Down French Onion Tart

Name: Upside Down French 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; 1/2 teaspoon flaky sea salt; 1/2 teaspoon ground black pepper; 6 to 8 sprigs fresh thyme; 3 ounces Gruyère cheese, thinly sliced; 1 sheet frozen puff pastry, thawed; 1 large egg beaten with 1 teaspoon water; Balsamic glaze for serving (optional)

This elegant appetizer features caramelized onion discs, melted Gruyère, and flaky puff pastry for a sophisticated snack that is surprisingly simple to make.

By Enzo81 Kitchen· French· October 20, 2026

easy.enzo81.xyz

Prep

20 minutes

Cook

30 minutes

Total

50 minutes

Serves

9 to 12 squares

French cooking has a reputation for being fussy, but some of the best recipes are actually quite simple. My favorite dishes are the ones that take a humble ingredient like the onion and turn it into something special. This upside down tart is inspired by my travels through the Alsace region, where simple, rustic ingredients create something truly memorable.

The secret to this recipe is the upside down method. By layering honey and onions on the baking sheet before placing the puff pastry on top, the onions caramelize beautifully while the oven heat works its magic. It is a fantastic party appetizer that looks like you spent all day in the kitchen.

Ingredients

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

9Instructions

1
Preheat your oven to 400 degrees Fahrenheit and line a rimmed baking sheet with parchment paper.
2
Peel the onions and slice them crosswise into 1/4 inch thick rings, keeping the layers together to form onion discs.
3
Place 6 small patches of olive oil on the parchment paper in two rows of three.
4
Drizzle the honey over each oil patch, then sprinkle with the salt, pepper, and a small thyme sprig.
5
Arrange the larger onion discs over these patches, then fill in the gaps with the remaining smaller onion slices until the area is covered.
6
Lay the Gruyère slices evenly over the onions.
7
Place the puff pastry sheet over the entire arrangement and tuck in the edges if necessary.
8
Brush the top of the pastry with your egg wash and bake for about 30 minutes, or until the pastry is puffed and golden brown.
9
Let the tart cool for 5 minutes, then carefully flip it over onto a serving board and garnish with fresh thyme leaves or a drizzle of balsamic glaze.

Tips

Serve this tart warm, cut into squares for easy grabbing. If you have leftovers, you can store them in an airtight container in the fridge and reheat them in a low oven to keep the pastry crisp.

#vegetarian #appetizer #french #party food #easy recipe

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