Ingredients:

  • 2 Tbsp Unsalted Butter
  • 2 large Leeks, white and light green parts only, trimmed, sliced thinly, and washed well (Approx. 400 g)
  • 12 oz Mixed Mushrooms (e.g., Cremini, Shiitake), cleaned and roughly chopped (340 g)
  • 1 tsp fresh Thyme leaves, stripped from the stem
  • 2 Tbsp Dry Sherry or Dry White Wine
  • 1 Tbsp All-Purpose Flour
  • ½ cup Heavy Cream (120 ml)
  • 3 oz Gruyère Cheese, grated (85 g)
  • Salt and Black Pepper, To taste
  • 2 sheets All-Butter Puff Pastry (Approx. 450 g)
  • 1 large Egg
  • 1 tsp Water

Instructions:

  1. Sauté the Aromatics: Melt the butter over medium heat. Add the sliced leeks and sauté until soft and translucent (about 5–7 minutes). Season lightly.
  2. Cook the Mushrooms: Add the mushrooms and thyme to the pan. Increase heat and cook until the mushrooms have released their liquid and the liquid has completely evaporated (8–10 minutes).
  3. Deglaze and Thicken: Pour in the Sherry or Wine, scraping up any fond. Cook for 1 minute. Sprinkle in the flour, stirring continuously for 1 minute.
  4. Create the Base: Stir in the heavy cream and bring to a simmer until thickened slightly. Remove from heat.
  5. Finish and Chill (Critical Step): Stir in the grated Gruyère until melted. Season aggressively with salt and pepper. Transfer the filling to a shallow bowl and chill completely in the refrigerator (45 minutes minimum). The filling must be stone cold before assembly to prevent the pastry from melting.
  6. Cut the Discs: Unroll the puff pastry. Use a 6-inch (15 cm) circular cutter to cut 4 base discs. Use a 7-inch (18 cm) cutter to cut 4 top discs. Place all 8 discs on a parchment-lined baking sheet.
  7. Position the Filling: Place one spoonful of chilled filling onto the center of each smaller base disc, leaving a generous 1-inch (2.5 cm) border clear around the edge. Ensure the filling is piled neatly into a dome shape.
  8. Moisten and Seal: Whisk the egg and water to make the egg wash. Lightly brush the pastry border of the base disc. Place the larger top disc over the filling. Press down gently from the center outwards to eliminate air pockets.
  9. Flute the Edges: Use the blunt side of a small knife or your fingers to press and crimp the edges firmly together, creating a decorative fluted or scalloped seal. This seal must be watertight. Rest the assembled pithiviers back into the refrigerator for 15 minutes to firm up the edges.
  10. Prepare for Baking: Preheat oven to 400°F (200°C / Gas Mark 6).
  11. Glaze and Score: Brush the entire surface of the chilled pithiviers with egg wash (do not allow the wash to drip down the sides). Use the tip of a paring knife to gently score a spiral design starting from the center outwards, taking care not to pierce all the way through the top layer of pastry.
  12. Bake and Adjust Heat: Bake for 15 minutes at 400°F (200°C). Lower the oven temperature to 375°F (190°C / Gas Mark 5) and continue baking for another 13–17 minutes, until deep golden brown and well-puffed.
  13. Serve: Allow to cool slightly (5 minutes) before serving.