Lyonnaise Salmon in Brioche

Make the brioche: whisk flour, yeast, sugar, and salt together in a stand mixer bowl. Add the 3 whole eggs and 3 yolks and mix on medium speed with the dough hook for 8 minutes until the dough is smooth and pulls away from the sides.

Add the softened butter cubes a few at a time with the mixer running on medium, waiting until each addition is fully incorporated before adding the next — this should take about 10 minutes total. The finished dough will be glossy and elastic.

Shape the dough into a ball, cover the bowl tightly with cling film, and refrigerate for a minimum of 8 hours and up to 24 hours.

Make the duxelles: melt 30 g butter in a wide skillet over medium-high heat until foaming subsides. Add the shallots and cook, stirring, for 3 minutes until softened and translucent.

Add the garlic and mushrooms and cook, stirring frequently, for 8–10 minutes until all moisture has evaporated and the mixture is dry and darkened — it should not steam any longer.

Pour in the vermouth and cook for 1 minute until fully absorbed. Remove from heat, stir in the tarragon and parsley, season with ½ tsp salt and ½ tsp white pepper, and spread on a plate to cool completely.

Season the salmon fillet all over with the remaining 1½ tsp salt and ½ tsp white pepper. Brush the top and sides generously with the Dijon mustard, then press the cooled duxelles firmly over the mustard-coated surface to form an even layer.

Remove the brioche dough from the refrigerator. On a lightly floured surface, roll it out to a rectangle approximately 35 × 28 cm and about 4 mm thick.

Place the salmon fillet duxelles-side down in the centre of the dough. Fold the long sides of the dough up over the fish, then fold the short ends over and press firmly to seal, trimming any excess dough so seams are no thicker than two layers. Turn the parcel seam-side down onto a parchment-lined baking tray.

Beat the remaining whole egg with 1 tsp cold water and brush the entire surface of the parcel. Refrigerate uncovered for 20 minutes to set the glaze and firm the dough.

Preheat the oven to 200°C, or 180°C for a fan oven, or gas mark 6 while the parcel chills.

Brush the parcel with a second coat of egg wash. Score the top lightly with a sharp knife in a leaf or crosshatch pattern, cutting no deeper than 1 mm.

Bake on the middle shelf for 28–32 minutes until the brioche is a deep mahogany brown and the internal temperature of the salmon registers 63°C on a meat thermometer inserted through the side of the parcel into the thickest part of the fish.

Transfer to a wire rack and rest for 8 minutes before slicing with a serrated knife at the table.