Strain the blackberry jam through a fine sieve into a tall mixing beaker. Peel half the banana and, broken into pieces, add to the jam with the squeeze of lemon juice.
Core the washed plums and add finely chopped. Pour in the milk and puree everything finely with the blender.
The result is a rather creamy liquid. If you want the drink to be more liquid, just stir in some milk. Pour the drink into a glass, garnish and serve.