Crumble the biscuits, to them add the crushed walnuts and melted butter. Stir until the ingredients are mixed.
Put the resulting mixture in a cake form with removable sides and spread it out. Put it in the fridge to cool. In the meantime, make the cream.
Stir with a spatula or spoon. Pour the mixture onto the cake layer and leave it in the fridge for at least 2 hours until hardened.
Once it's ready, pour on the jar of blueberry jam and spread it out all over it. Return to the fridge and serve cooled.