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. "
Adding "and a half" to a noun is a slang way of adding emphasis, a device that is pretty popular and common in AmE. A treat and a half just means a really nice treat, but the expression can be applied to many nouns. For example, if my friend has a dog that is very big, or outstandingly canine in some other way, I could say "That's a dog and a half." However, I recommend that learners avoid it. As with much slang, there are subtle nuances governing when it is appropriate and when it is not.