Start this recipe by preparing the loaf tin by coving the inside with a piece of cling film. Next, soak the gelatine leaves in a bowl of water. When soft, place into a saucepan with 2 tablespoons of water and melt to dissolve. Put aside. Whilst the chocolate is melting, whisk the egg whites and lemon juice in a large, clean bowl until they form soft peaks. The lemon juice will stabilise the egg whites, make them easier to work with. Add the sugar and continue to whisk until firm peaks form when the whisk is removed. In another bowl, whisk the cocoa powder and the fresh cream together to soft peaks and put aside. When the chocolate has cooled down slightly, whisk in half of the egg whites quickly, stirring vigorously until thick and well combined. Fold in the remaining egg whites into the chocolate mixture, using a spatula, until all of the egg white has been completely incorporated, followed by the whipped chocolate fresh cream. Quickly spoon 1/3 of the mousse mixture into the base of the prepared tin and even out. Cover with a layer of the `After-eight` mints. Cover again with another 1/3 of mousse and mints, followed by the remaining cream. Finally, cover the top evenly with a final layer of mints. Wrap over the excess cling film and chill in the freezer for an hour, or until set. Carefully place the parfait on a long serving plate and decorate with chocolate straws and mint leaves.