Upside-Down French Onion Tart

An upside-down puff pastry tart topped with red onions, Gruyère, honey, thyme, and balsamic glaze. Preparation/total time includes an estimate based on the recipe steps; the creator did not specify every timing field.

By @wellplated

Original recipe source

Cook time: 30 minutes

Servings: 9

Ingredients

• 2 onions small/medium red onions peeled and sliced crosswise 1/4-inch thick through the equator into rings
• 2 tablespoons extra-virgin olive oil
• 4 tablespoons honey or hot honey
• 0.5 teaspoon flaky sea salt
• 0.5 teaspoon ground black pepper
• 6 sprigs fresh thyme plus fresh leaves for serving
• 0 flaky sea salt (to taste) Source specifies seasoning to taste
• 0 ground black pepper (to taste) Source specifies seasoning to taste
• 3 ounces Gruyère cheese thinly sliced
• 1 sheet frozen puff pastry thawed according to package directions
• 1 egg large egg beaten with 1 teaspoon water to create an egg wash
• 0 flaky sea salt (to taste) Source specifies seasoning to taste

Instructions

1. Preheat the oven to 400°F. Line a rimmed baking sheet with parchment paper. Oven is at 400°F and the baking sheet is lined.
2. Peel the onions, then slice them crosswise 1/4-inch thick through the equator (not the ends) so that you create rings. Try to keep the layers in each slice together so you have onion discs. Onion rings are sliced and kept in disc-like layers.
3. Create 6 drizzle patches of olive oil spaced evenly over the parchment in 2 rows of 3. Six olive oil patches are spaced on the parchment.
4. Drizzle the honey over the oil, then sprinkle each patch with a pinch of flaky salt and black pepper. Lay a small thyme sprig across each one. Each patch is topped with honey, seasoning, and thyme.
5. Find your largest onion discs and lay one over each patch. Then, take the smaller discs and fill in the gaps. Almost no parchment should peek through; a little overlap is fine. The onion layer fully covers the patches.
6. Lay the Gruyère slices over the onions, spacing them evenly and leaving a border of at least 1 inch on all sides. Gruyère is evenly distributed with a border left clear.
7. Unfold the puff pastry on a lightly floured work surface. Roll it into a rectangle about 2 inches longer than the onions on each side (mine was 10 by 13). Gently drape the pastry over the onions. With the tines of a fork, press the edges of the pastry all the way around to create a border. Pastry is draped over the tart and the border is sealed.
8. Brush the pastry lightly with the egg wash. Dab up any pools that collect with a paper towel. Pastry is lightly brushed with egg wash.
9. Bake the onion tart for 25 to 30 minutes on the center rack, until the pastry is deeply golden and puffed. Pastry is deeply golden and puffed.
10. Let rest 5 to 10 minutes. Set a large cutting board on top of the pan. Working quickly and confidently, flip the board and tart over together so the tart is now sitting on the board. Lift off the pan and peel away the parchment. Drizzle with balsamic glaze, scatter with fresh thyme leaves and flaky salt, and slice into squares. Tart is inverted, garnished, and sliced.