Butter 4 large pieces of foil. Separate the pak choi leaves and thickly slice the larger ones. Trim the asparagus and cut each stem into 2 or 3 pieces depending on length. Divide the vegetables between the pieces of foil and place a salmon fillet on top of each one.
Divide the remaining butter between the salmon fillets, sprinkle with the ginger and a little seasoning then drizzle with Pernod. Bring the foil up and over the salmon and seal well. Chill the parcels until required.
When ready to serve, cook the parcels on a baking sheet in a preheated oven, 180°C (350°F), Gas Mark 4, for 25 minutes. Unwrap one of the parcels and pierce the centre of the salmon. If it flakes easily and the flakes are all one colour they are ready, if not, cook for a few more minutes and then retest. Transfer the salmon and vegetables to shallow serving bowls and serve with plain boiled rice.