@Clevesian
I came back to say I finally tried this recipe again.
I halved the recipe in case it was a disaster again though, as I didn’t want to waste too many ingredients.
I also made my own caramel from condensed milk instead of using the can of caramel. This meant I could make it thicker, I find the tin very runny.
Anyhow, happy to report that spreading the layers much, much thinner meant it was a success this time. It went down well and everyone who tried it raved about it. There have been requests for me to make it again so I will use the full recipe next time, and use an even bigger tin than I did the first time around.