In a blender, combine the strawberries (reserve a few slices for garnish), sugar and lemon juice. Puree until smooth. Push the berry mixture through a sieve and discard the seeds. Using an electric mixer, whip the cream just until stiff peaks form. Take a large spoonful of the whipped cream and stir it into the strawberry puree to lighten the mix. Fold the strawberry mixture gently into the whipped cream. Gently spoon the fool into a chilled serving bowl and garnish with the reserved strawberries and mint leaves. Refrigerate before serving, at least 1 hour and up to 4 hours.