[Sundae]

I assume it was only my ignorance which stopped me realising that the lemon mixture should be heated? I Googled other recipes in the end and saw that this was part of the procedure. I honestly thought that some chemistry in the ingredients would cause it to thicken; hey, some things do, right? If it really was supposed to thicken cold, then I've no idea what I did wrong, because I added the lemon juice by the teaspoon and with every teaspoon it just became more dilute.

I very nearly gave up, but the egg count and the cost of the condensed milk was already so high I had to carry on. Note, high by my standards five days before payday.

I went for an Italian style meringue in the end.
I was a little wary of knowing how much sugar to add, having already proved myself an incompetent baker. So I picked an online recipe with detailed amounts. Sadly I couldn't find any which used 4 egg whites, and I'd already separated them, so I had to double up on the other amounts and was left with a mountain of meringue (and I know you said this might be the case anyway, Ali.)
Ditto lemon custard stuff.
Yes I could have made another batch of cakes to use it up but by then I was too weary. I hate to fail at things. And I'd been up since 04.45.

Mum said she likey, but if I made again I would SO use lemon curd (shop bought!) and a traditional meringue. Which is what you suggested Ali.

Leftover lemon sauce and meringue mix.