Caramelized Onion, Gruyère & Thyme Rough-Puff Palmiers

Instructions

1. 1

   In a wide mixing bowl, whisk 250 g all-purpose flour and 0.5 tsp fine sea salt. Add 200 g unsalted cultured butter, cut into 1/2-inch cubes. Toss the cubes to coat with flour, then press each cube flat between your thumbs and index fingers into thin walnut-sized shingles. Drizzle in 110 ml ice water. Use a bench knife or a flexible spatula to turn the mixture over itself until a shaggy, uneven dough forms with visible butter chunks. Do not knead.

   10 min

   Tip: Visible butter sheets are your steam pockets; over-mixing will melt them into the dough and kill your lift.

2. 2

   Tip the shaggy dough onto a lightly floured counter. Press into a rough rectangle. Using a floured rolling pin, roll the dough into a 6x15-inch strip. Fold the top third down, then the bottom third up like a business letter (turn one). Rotate the dough 90 degrees. Roll out again into a 6x15-inch strip, and fold into thirds once more (turn two). Wrap tightly in parchment or plastic and transfer to the refrigerator to chill for 30 minutes.

   8 min

   Tip: If the butter feels sticky or smudges into the bench at any point, slide the dough onto a tray and freeze for 5 minutes.

3. 3

   While the dough chills, melt the remaining 25 g unsalted cultured butter in a wide heavy skillet over medium-low heat. Add 2 large yellow onions, 0.5 tsp fine sea salt, and 2 tsp fresh thyme leaves. Cook low and steady, stirring occasionally, until the onions collapse, release their liquid, and turn a rich, translucent caramel amber, about 22 minutes. Deglaze the pan with 1 tbsp sherry vinegar, scraping up all the sticky browned fond. Remove from the heat, spread onions on a flat plate, and chill in the freezer for 5 minutes to cool completely.

   25 min

   Tip: The onions must be cold and dry before hitting the dough. Hot onions melt butter instantly and turn puff pastry soggy.

4. 4

   Remove the chilled rough puff from the fridge onto a lightly floured surface. Roll the dough into an even 10x14-inch rectangle, about 1/8-inch thick. Use an offset spatula to spread 2 tbsp Dijon mustard in a thin, sheer layer edge-to-edge across the surface. Scatter the cooled caramelized onions evenly over the mustard. Top with 100 g Gruyère cheese, the remaining 1 tsp fresh thyme leaves, and 0.5 tsp freshly cracked black pepper.

   8 min

   Tip: Keep the mustard layer gossamer-thin so the pastry doesn't steam from excess moisture.

5. 5

   Fold the long edges of the dough inward so they meet halfway toward the center line. Fold them inward once more so the two folded edges touch snugly along the center seam. Finally, close the two halves together like a book to create an eight-layer palmier log. Press down gently with a rolling pin to seal. Wrap the log and chill in the refrigerator for 15 minutes to firm up the butter before slicing.

   18 min

   Tip: Firm pastry cuts cleanly without squishing the interior layers together.

6. 6

   Position racks in the upper and lower thirds of the oven and preheat to 400°F (205°C). Line two heavy rimmed baking sheets with parchment paper. Using a sharp chef's knife, slice the chilled log into 1/2-inch-thick cross-sections (about 16 to 18 pieces). Place them cut-side up on the prepared sheets, leaving 2 inches between each palmier. Gently flare the top two wings open slightly in a 'V' shape to give them room to expand sideways as they puff.

   8 min

   Tip: Use a gentle sawing motion with a very sharp blade; do not press straight down or you'll blunt the edges.

7. 7

   Bake at 400°F (205°C) for 16 minutes. Remove the sheets from the oven, quickly flip each palmier over using a thin metal spatula, and swap sheet positions from top to bottom. Bake for another 8 to 10 minutes until deeply golden brown, with bubbling caramelized cheese skirts and crisp, lacy edges.

   26 min

   Tip: Flipping midway ensures the underside gets directly glazed by the melting cheese and caramelized onion sugars.

8. 8

   Transfer the hot palmiers immediately to a wire cooling rack. Sprinkle warm pastries with 0.5 tsp flaky sea salt. Let them cool for 5 to 10 minutes until the melted cheese firms up and the pastry shatters under light pressure. Serve warm or at room temperature.

   5 min

   Tip: Don't leave them cooling on the baking parchment or the sugar-cheese lacework will stick permanently.