Peel and halve the avocado, discarding the pit. Cut avocado into rough pieces. Place the avocado and one cup of the stock in the container of an electric blender. Add the curry powder, salt and pepper. Blend at high speed for thirty seconds.
Pour mixture into an enamelware saucepan. Add remaining stock and heat, stirring, to boiling. Cool. Stir in cream and chill.
Serve in chilled soup cups. Garnish each serving with an avocado slice dipped into lemon juice to prevent discoloration.