Method

• 1.
  Heat 2 tbs olive oil in a frypan over medium heat. Add onion, season, then cook, stirring for 5 minutes or until softened. Reduce heat to medium-low, and cook, stirring, for a further 20-25 minutes until slightly caramelised. Remove onion from pan and season. Set aside to cool.
• 2.
  Wipe pan clean, then return to medium heat. Add butter and remaining 1 tbs oil. Add mushroom and cook, stirring, for 5-6 minutes until golden and softened. Remove from pan and set aside.
• 3.
  Blanch silverbeet in a pan of boiling water for 2 minutes or until wilted. Drain and refresh in cold water. Set aside.
• 4.
  Roll out one pastry sheet on a lightly floured surface until slightly larger than the trout. Place the pastry on a baking paper-lined baking tray and spoon onion down the centre, so it is the same width as the trout. Season trout, then place on top of onion. Spread over mushrooms, then top with silverbeet and sliced egg. Brush edges of pastry with egg wash. Roll out the second sheet of pastry until slightly larger than the trout. Place over trout, pressing edges to seal. Trim excess pastry, then chill for 30 minutes.
• 5.
  Meanwhile, for the cream, soak saffron in 1/4 cup (60ml) boiling water until cool. Whiz egg yolks, mustard and vinegar in a food processor until combined. With the motor running, gradually add the oil in a steady stream until thick and emulsified. Transfer to a bowl with the saffron-infused water and whisk to combine. Season, then chill until ready to serve.
• 6.
  Preheat the oven to 200°C. Brush the coulibiac with remaining beaten egg, then bake for 40-45 minutes until golden.
• 7.
  Serve the coulibiac warm, drizzled with the saffron cream.