Preheat the oven to 220°C.
Line a 1kg loaf tin with cling film, ensuring overhang for later coverage.
Slice the salmon fillet into three thick pieces sized to fit the tin.
Place salmon on a tray and coat with goose fat.
Cook in the oven for five minutes then allow to cool completely.
Beat the butter and chopped chives together and season with salt and pepper.
Line the base and sides of the tin with a quarter of the smoked salmon.
Place a piece of cooked salmon in the tin and spread a third of the chive butter over it.
Repeat layers of smoked salmon, cooked salmon, and chive butter, ending with smoked salmon.
Press the terrine down firmly, cover with cling film, and chill for at least one hour.
Whisk lemon juice and olive oil together and toss with salad leaves and seasoning.
Unwrap the terrine and carefully transfer it to a serving plate.
Slice the terrine and serve immediately with the dressed salad.