There are slight variations on recipes but the standard is
1kg white sugar
1 ( aprox 400g) tin of condensed milk
100g unslated butter
Some recipes use a lot of water some will use more milk.
I won't type out what I did because I don't actually think it was really right, however, I found THIS RECIPE while searching and I think she explains it so well. The recipe I followed was almost this, but not quite. When I make it again (probably in about 10 years once we've recovered from this sugar rush - I'm sure I can feel a migraine coming on!!) I'll do it her way.
I just have no clue how we're going to manage to eat it all.
I wonder how long it lasts?
Here it is simmering away.
And the colour change. The far right is the totally uncooked mixture. I actually did did four tests in total. You can see the mixture gets darker the longer it's cooked.
And the finished article