If I remember correctly it was for the chocolate bar 'Topic' - slogan: 'There's a hazelnut in every bite'. I think it was a cartoon or animated character voiced by Bill Oddie, with some dialogue which ended as per the question.
The animated character was called Toby and the slogan was hidden behind the Topic. Toby was supposed to recite the slogan but wasn't able to, he then ate the Topic a bite at a time revealling more of the slogan each time and attempting to get it right. I particularly remember 'a happy birthday to Toby' as he had revealed 'A ha..' It culminated with the quote in the original question after he had eaten all the chocolate.
Good grief I must have watched a lot of telly!