In a frypan, melt butter & saute onion until soft.

Place sauteed onion, oysters or mussels, lemon juice & tomato paste or sauce in a food processor or blender & process until the mixture forms a smooth puree.  Add cream cheese & process to combine.

If a food processor or blender is not available, push oysters or mussels through a sieve & beat into the onion, lemon juice, tomato paste or sauce & cream cheese.

Dissolve gelatine in boiling water & combine with cream cheese mixture.

Whip cream until soft peaks form.  Beat egg white until stiff.  Fold cream into cream cheese mixture, then fold in egg white.

Pour mixture into a greased mould, smoothing the top.  Chill until set, then unmould onto a serving plate.

Garnish if desired, with slices of cucumber & fresh parsley.  Serve with crackers or thin slices of toast.