Whisk the double cream and icing sugar to soft peaks. Fold through the coffee essence and vanilla extract. Toast the walnut halves in a dry frying pan for 2 mins until just golden, then set aside to cool. Roughly chop the toasted walnuts and fold half through the coffee cream. Layer the coffee cream mixture into dessert glasses with the remaining chopped walnuts, crushed meringue nests and cubed coffee walnut cake, then serve.