Bouchées à la Reine aux Champignons et Gruyère

Place the dried porcini in a small bowl and pour over the boiling water; set aside to soak for 20 minutes. Finely dice the shallot, mince the garlic, slice the fresh mushrooms, grate the Gruyère, and strip the thyme leaves.

Once soaked, lift the porcini out, chop roughly, and strain the soaking liquid through a fine sieve lined with kitchen paper — reserve 80 ml of the liquid. Cover and set aside while you prepare the remaining components.

Preheat the oven to 200°C (180°C fan / gas 6). Brush the tops of the vol-au-vent shells lightly with the beaten egg yolk, avoiding the cut sides so they can rise freely, and place on a lined baking tray.

Bake the vol-au-vent shells for 12–15 minutes until deep golden and crisp. Remove from the oven, carefully lift or press out any inner pastry caps, and set the shells aside on the tray.

Melt 30 g of the butter in a wide sauté pan over high heat. When the foam subsides and the butter smells nutty, add the fresh sliced mushrooms in a single layer and cook undisturbed for 2–3 minutes until deeply browned on one side, then season with salt and toss.

Add the chopped porcini and thyme to the pan, stir to combine, and cook for a further 2 minutes until fragrant. Transfer the mushroom mixture to a bowl and set the pan aside.

Return the pan to medium heat and melt the remaining 30 g of butter. Add the shallot and a pinch of salt, cooking for 3–4 minutes until completely softened and translucent.

Add the garlic and cook for 1 minute until fragrant but not coloured.

Add the flour all at once and stir constantly with a wooden spoon for 2 minutes to cook out the raw flour — the roux should turn a pale golden colour and smell biscuity.

Add the sherry and stir vigorously for 1 minute, scraping up any bits from the base of the pan, until the liquid is mostly absorbed.

Add the warm milk in a slow, steady stream, whisking constantly to prevent lumps, then add the reserved 80 ml porcini soaking liquid. Cook over medium heat, stirring continuously, for 4–5 minutes until the sauce thickens enough to coat the back of a spoon.

Remove the pan from the heat. Stir in the crème fraîche, then add two-thirds of the Gruyère, stirring until fully melted and smooth. Season generously with salt, pepper, and the nutmeg.

Fold the sautéed mushroom mixture back through the sauce until evenly combined.

Reduce the oven temperature to 180°C (160°C fan / gas 4). Spoon the filling generously into and slightly mounding over each vol-au-vent shell. Scatter the remaining Gruyère over the tops.

Return to the oven for 8–10 minutes until the filling is bubbling at the edges and the cheese on top is golden and beginning to blister. Scatter with fresh parsley and serve immediately.