In a saucepan, melt 125g butter or margarine with 60g chocolate. Remove from the heat and stir in white sugar, egg, rolled oats, coconut, chopped nuts and 1 teaspoon vanilla essence. Press mixture into a greased 23cm square pan and chill for 1 hour.
Combine icing sugar with 3 tablespoons softened butter, 1/2 teaspoon of the vanilla and milk. Mix until it has an icing-like consistency and spread it over the oat mixture in the pan. Chill for 1/2 hour.
Melt remaining 1 tablespoon butter or margarine with remaining 60g chocolate. Spread over the top of the bars. Chill for 4 to 5 hours.
Cut into squares using a hot knife; dip knife in hot water and let it melt through the chocolate.