Preheat the oven to 180C/350F/Gas 4.
Place the fresh salmon on a square of foil. Season with salt and pepper. Fold over the foil to make a parcel. Cook in the oven for 12-15 minutes, or until the flesh has turned to an opaque pink. Remove from the oven and leave to cool.
Remove the woody end from the asparagus and trim to exactly the length of the loaf tin. Bring a frying pan of water to the boil and cook the asparagus stems for 3-4 minutes, or until they feel just tender when pierced with a knife. Drain and plunge into a bowl of ice-cold water to cool. Drain and pat dry.
Grease the loaf tin, then line with a double layer of cling film. Open the pack of smoked salmon and separate the slices. Trim one slice to fit the base of the tin, and then cut slices to fit all four sides, leaving a little to overhang. Reserve one slice for the top.
Place the remaining smoked salmon in a food processor with the cold cooked salmon, cream cheese, very soft butter, chives and lemon juice. Blend until smooth and season to taste.
Spread half of the smoked salmon mixture into the lined tin and top with the asparagus spears, laying head to tail so that they fit tightly into the tin. Top with the remaining salmon mixture and lay the last piece of smoked salmon on top.
Cover the terrine with cling film and leave to chill for at least six hours in the fridge, then turn out, remove the cling film and cut into slices. Scatter with cress and serve with toast or salad.