🍄 Upside-Down French Onion & Mushroom Tarts
Crispy puff pastry, deeply caramelized onions, salty Gruyère, beautiful gourmet mushrooms, hot honey + flaky salt. Basically everything I want in an appetizer.
Makes 6
YOU’LL NEED
* 1 sheet puff pastry, thawed but kept cold
* 10–12 oz gourmet mushrooms — I used black pearl + chestnut
* 2 large yellow onions, thinly sliced
* 1 cup freshly grated Gruyère
* 2 Tbsp butter, divided
* 2 Tbsp olive oil, plus more as needed
* 1 tsp fresh thyme leaves + more for finishing
* 2 Tbsp dry sherry or white wine
* 1 tsp Worcestershire sauce
* Kosher salt + freshly cracked black pepper
* 1 egg + splash of water, for egg wash
* Hot honey
* Flaky sea salt
MAKE THE ONIONS 🧅
Heat 1 Tbsp butter + 1 Tbsp olive oil over medium-low. Add onions and a good pinch of salt. Cook slowly for 30–45 minutes, stirring occasionally, until deeply golden, soft and jammy.
Add thyme, black pepper, sherry and Worcestershire. Cook until the liquid has completely evaporated. Set aside to cool.
SEAR THE MUSHROOMS 🍄🟫
Tear larger mushrooms into beautiful clusters and halve smaller mushrooms if needed.
Heat 1 Tbsp olive oil in a skillet over medium-high/high heat. Add mushrooms in a single layer and let them develop a deep golden sear before moving them.
Add remaining 1 Tbsp butter, season with salt and pepper and cook just another minute or two. They’ll finish in the oven. Cool slightly.
ASSEMBLE
Heat oven to 400°F and line a sheet pan with parchment.
Cut cold puff pastry into 6 rectangles.
For each tart, layer directly onto the parchment:
thyme → mushrooms, pretty side DOWN → caramelized onions → Gruyère → puff pastry
Gently press the pastry around the filling and against the parchment. Poke a tiny vent in the top.
Whisk egg with a splash of water and brush over the pastry.
BAKE
Bake for 20–25 minutes, until the puff pastry is deeply golden, crisp and puffed.
Rest for about 2 minutes, then slide a spatula underneath each tart and FLIP. ✨
Finish while warm with hot honey, fresh thyme and flaky sea salt.
That combination of earthy mushrooms, sweet French onions, creamy-salty Gruyère and that little hit of sweet heat at the end is 🤌.
SAVE this one for your next dinner party, holiday gathering or whenever you need an appetizer that looks considerably harder to make than it actually is.
