Caramelized Onion, Mushroom and Fontina Tart with Arugula Salad

Steps

1. Step 1

   Melt 2 tbsp of the butter with the olive oil in a large skillet over medium heat. Add the sliced onions, the sugar and a generous pinch of salt. Stir to coat.

   5 min

   • 2 tbsp unsalted butter
   • 1 tbsp olive oil
   • 2 lb yellow onions (about 3 large)
   • 1 tsp granulated sugar
   • kosher salt
2. Step 2

   Cook the onions, stirring every few minutes, until deep golden brown, soft and jammy, 30 to 35 minutes. Lower the heat if they start to scorch, and add a splash of water to loosen any browned bits. Scrape them into a bowl.

   35 min

3. Step 3

   Meanwhile, heat the oven to 400°F and line a large rimmed baking sheet with parchment paper.

   400°F

4. Step 4

   Wipe out the skillet and melt the remaining 1 tbsp butter over medium-high heat. Add the mushrooms and a pinch of salt and cook, stirring only occasionally, until browned and no liquid is left in the pan, 7 to 9 minutes. Add the garlic and thyme and cook 1 minute, then pour in the wine and stir until it has evaporated. Season with salt and pepper and set aside.

   10 min

   • 1 tbsp unsalted butter
   • 10 oz cremini mushrooms
   • 2 cloves garlic
   • 1 tsp fresh thyme leaves
   • 2 tbsp dry white wine or water
   • kosher salt
   • black pepper
5. Step 5

   Unfold the pastry on a lightly floured surface and roll it into a roughly 10x15 in rectangle. Transfer it to the lined baking sheet. With a knife, score a border 3/4 in in from the edge all the way around, cutting only halfway through the pastry. Prick the inside of the border all over with a fork. Brush the border with the beaten egg.

   10 min

   • 1 piece frozen puff pastry sheet (about 9-10 oz)
   • 1 egg
6. Step 6

   Scatter about two-thirds of the Fontina inside the border. Spread the caramelized onions over the cheese, then scatter the mushrooms on top. Finish with the remaining Fontina and a few grinds of black pepper.

   5 min

   • 6 oz Fontina cheese
   • black pepper
7. Step 7

   Bake until the pastry is puffed and deep golden at the edges and the cheese is bubbling, 25 to 30 minutes. Let the tart rest on the sheet for 5 minutes.

   30 min, hands-off · 400°F

8. Step 8

   While the tart bakes, whisk the balsamic vinegar, Dijon and a pinch of salt in a large bowl, then whisk in the extra-virgin olive oil. Just before serving, add the arugula and toss to coat; top with shaved Parmesan if using.

   5 min

   • kosher salt
   • 1 tbsp balsamic vinegar
   • 1 tsp Dijon mustard
   • 2 1/2 tbsp extra-virgin olive oil
   • 5 oz baby arugula
   • 2 tbsp shaved Parmesan
9. Step 9

   Slide the tart onto a board, cut into 4 pieces and serve warm with the arugula salad alongside or piled on top.

Where it’s from

Written by AI from an idea

Version 1, saved Oct 4, 2026