Aged Gruyère, Delicata Squash & Dijon Rough-Puff Dartois

Instructions

1. 1

   Preheat your oven to 400°F (205°C). Toss 1 medium delicata squash slices on a baking sheet with 1 tbsp extra-virgin olive oil, 0.5 tsp fine sea salt, and 0.5 tsp freshly ground black pepper. Spread into a single layer and roast for 18 to 20 minutes until tender with caramelized edges. Let cool completely on the sheet pan.

   20 min

   Tip: Leave the skin on! Delicata skin is paper-thin and softens completely in the heat, adding texture and skipping fussy peeling.

2. 2

   In a wide mixing bowl, whisk together 240 g all-purpose flour and the remaining 0.5 tsp fine sea salt. Toss in 225 g unsalted cultured butter. Using your fingers or a pastry blender, press the cubes flat into thin walnut-sized sheets—do not rub them down into fine meal. Stir 1 tsp apple cider vinegar into 120 ml ice water, then drizzle it over the flour. Use a flexible bench scraper to fold the mixture together until a shaggy, ragged dough just clings together.

   8 min

   Tip: Big, visible shingles of butter are the secret. As that trapped moisture turns to steam in the oven, it lifts the dough into airy, lacy sheets.

3. 3

   Tip the shaggy mass onto a lightly floured surface. Press it into a rough 6x10-inch rectangle. Roll gently into a 8x15-inch strip. Fold the top third down and the bottom third up, just like a business letter (un tour simple, or a single letter fold). Turn the dough 90 degrees, roll out to 8x15 inches again, and repeat the letter fold once more. Flatten into a compact 5x7-inch block, wrap tightly in parchment, and chill in the refrigerator for 25 minutes.

   7 min

   Tip: If the butter ever feels soft or smears greasy instead of rolling, slide the board straight into the freezer for 5 minutes. Cold butter equals flake; warm butter equals dense dough.

4. 4

   Keep the pastry dough chilling in the coldest part of your refrigerator so the gluten relaxes completely and the butter firms up.

   25 min

   Tip: Let time do the work. Resting here guarantees your dough won't shrink or turn tight like a bad alibi when baked.

5. 5

   Line a large sheet pan with parchment. Unwrap the chilled pastry, cut it in half, and roll one piece into a 5x14-inch rectangle about 1/8-inch thick; transfer to the pan. Spread 2 tbsp Dijon mustard down the center, leaving a 1/2-inch border bare along all sides. Shingle the cooled squash slices over the mustard, then scatter 1 tbsp fresh sage leaves and 140 g aged Gruyère cheese on top. Roll the second piece of dough to the exact same dimension and drape it over the filling. Press the outer edges firmly to seal, then trim with a sharp knife to neaten.

   12 min

   Tip: Make sure your squash is completely cool before building, or it will melt the pastry butter prematurely.

6. 6

   Brush the top surface evenly with the 1 large egg wash. Use the back of a paring knife to score diagonal crosshatch marks across the top crust, cutting lightly into the surface without piercing through the dough. Cut 4 small vent slits along the top. Sprinkle the remaining 30 g aged Gruyère cheese and 0.5 tsp flaky sea salt directly over the pastry. Chill the assembled pastry in the freezer for 10 minutes to set the lamination.

   10 min

   Tip: Freezing the fully assembled tart right before baking shocks the butter layers, giving you an explosive oven-spring.

7. 7

   Slide the chilled dartois into the 400°F (205°C) oven. Bake for 24 to 26 minutes, until the pastry is deep bronze, puffed high with visible layered ridges along the edges, and the Gruyère filling is aggressively bubbling through the vents.

   26 min

   Tip: Don't pull it out at pale gold. You want a deep café-grade chestnut color—that's where true caramelized depth and shatter live.

8. 8

   Let the dartois settle on the baking sheet for 5 minutes. Transfer to a cutting board and slice crosswise with a large serrated knife into 8 finger bars.

   5 min

   Tip: Saw through the pastry in swift, confident strokes with a serrated bread knife instead of pressing down, keeping those crisp layers pristine.