You will need to make this slice a day before you plan to serve it ... it needs time in the fridge to completely set before cutting, and once portioned it will keep in the fridge for at least five days.
The base is very firm so when portioning you will need a sharp knife. I like to cut the slice in sections, doing half the slice first so that it is easier for me to get nice even pieces. Once I have cut the whole slice, I keep it in two containers in the fridge ready to go, and only dust with icing sugar the portions I am actually serving at the time.
I cut this slice into 24 portions, but it can be divided up any way you like.
You will usually get approximately 50g to 60g juice from a lemon, so zest as many lemons as you need to get the total of 180g lemon juice for this recipe