Place condensed milk (1/2 cup) and butter (125g) in a saucepan. Stir over gentle heat until butter has melted and mixture has combined.
Crush biscuits very finely. Add lemon rind and coconut (1 cup). Mix well.
Add warm milk and butter mixture to the biscuit crumb mixture. Mix together with a wooden spoon.
Press mixture in greased lamington tin. Refrigerate for 1hr.
Icing: Combine sifted icing sugar, lemon juice, and soft butter (15g) in a bowl. Mix well until smooth. Spread over chilled biscuit base and sprinkle with coconut. Refrigerate until icing is set. cut into small squares
