Perfecting custard

I followed Delia's recipe for custard and mostly it went well, it eventually thickened up. It did look like it was splitting a little but I took it off the heat to rescue it and it came together again.
However, it did take a long time to thicken up and it had a slightly, almost foamy texture to it. Even the morning after, it hadn't set solidly the way you would expect it too, still with the same foamy texture.
I've only ever had birds custard so would the texture be different?
This was my first time making custard so didn't know if I've done something wrong.
Many thanks for any advice