Tart

• 1 sheet puff pastry (230 g / 8 oz), thawedFind substitute
• 2 large leeks, white and light green parts thinly sliced (300 g)Find substitute
• 6 shallots, thinly sliced (250 g)Find substitute
• 2 tbsp (30 g) unsalted butterFind substitute
• 1 tbsp (15 ml) olive oilFind substitute
• 1 tsp granulated sugarFind substitute
• 1 tsp kosher saltFind substitute
• ½ tsp freshly ground black pepperFind substitute
• 2 tsp fresh thyme leavesFind substitute
• ¼ cup (60 ml) dry white wineFind substitute
• ¾ cup (180 g) crème fraîcheFind substitute
• 1 large eggFind substitute
• 1 tbsp (15 g) Dijon mustardFind substitute
• 120 g (4 oz) blue cheese, crumbledFind substitute

Optional Finish

• 1 tbsp (15 ml) balsamic vinegar, optionalFind substitute
• 1 tbsp finely chopped fresh chives, optionalFind substitute

1. 1

   Heat the oven: Preheat the oven to 400°F (200°C). Line a large baking sheet with parchment paper.

2. 2

   Prepare the leeks: Separate and rinse the sliced leeks thoroughly in cold water to remove any trapped grit. Drain well and pat dry.

3. 3

   Caramelize the vegetables: Melt the 2 tbsp butter with the 1 tbsp olive oil in a wide skillet over medium heat. Add the leeks, shallots, sugar, salt, and black pepper. Cook for 18–22 minutes, stirring regularly, until very soft and golden. Reduce the heat if they begin browning too quickly.

4. 4

   Deglaze: Add the thyme and ¼ cup white wine. Cook for 2–3 minutes, stirring, until the wine has almost completely evaporated and the mixture is moist but not wet. If using the balsamic vinegar, stir in the 1 tbsp balsamic during the final 30 seconds. Remove from the heat and cool for about 5 minutes.

5. 5

   Blind-bake the pastry: Unroll the puff pastry onto the prepared baking sheet. Score a 1-inch (2.5 cm) border around the edge without cutting all the way through. Prick the center repeatedly with a fork, leaving the border untouched. Bake for 8 minutes. If the center puffs significantly, gently press it down with the back of a spoon.

6. 6

   Make the creamy base: While the pastry bakes, whisk together the crème fraîche, egg, and Dijon mustard until smooth.

7. 7

   Assemble: Spread the crème fraîche mixture evenly over the partially baked pastry inside the scored border. Distribute the leek-shallot mixture over it, then scatter the 120 g blue cheese evenly across the top.

8. 8

   Finish baking: Return the tart to the oven and bake for 15–18 minutes, until the filling is set and the pastry is crisp and deeply golden. Let rest for 5 minutes. If using the chives, sprinkle the 1 tbsp chopped chives over the tart before slicing into 4 portions.