I was wondering what does "a treat and a half" mean exactly? You can find many Google results of it, such as
"Peter Davison donates a treat and a half to the Doctor Who 50th celebrations."
"It's a treat and a half when a lovely new coffee shop opens just a few minutes walk away, nestled amongst the lanes."
"That was a treat and a half. I think the lace is fabulous and she was such a beautiful bride."
"An alternative to the cakes and pies, this double decker pudding is a treat and a half. "