No extra sugar required due to the sweetness of the condensed milk. You could add gelatine to help it set, but not necessary. If you want a thicker base then add more biscuits. You could even put the meringue on top of the cake to give it that bit extra crunch. Make sure you use a tin with either sprung sides or a push bottom or it will be impossible to get out.
I made it with double cream, zest and juice of 1 lemon. I didn't use condensed milk, vanilla extract, meringues, dark brown sugar and no lime. It was really delicious! The family loved it! - 19 Nov 2015