For the cake:
1) Preheat oven to 180C/Gas 4. Grease and flour 3 (20cm) round pans.
2) In a mixing bowl, cream the sugar and butter, mix until light and fluffy. Add the eggs 1 at a time and mix well after each addition. Mix cocoa and food colouring together and then add to sugar mixture; mix well.
3) Sift together flour and salt. Add flour mixture to the creamed mixture alternately with buttermilk. Blend in vanilla. In a small bowl, combine bicarbonate of soda and vinegar and add to mixture.
4) Pour batter into pans. Bake for 25 mins, or until a toothpick inserted into the centre comes out clean. Remove from heat and cool completely before icing.
For the icing:
1) Blend cream cheese and butter together in a mixing bowl. Add marshmallows and sugar and blend. Fold in coconut and nuts.
2) Spread between layers and on top and sides of cooled cake.