Nanaimo Bars? Hey they come from Vancouver Island, about 30 minutes from the camp I used to cook at. The "legend" is that a woman from Nanaimo entered her squares into a competition and when she got there she didn't have a name for them. The person registering her for the competition looked at her address and said how about Nanaimo bars. And the rest is history!
In my catering I make about 7 different flavours (including my signature cappucino and fresh raspberry varities) but the original is the TNT favourite.
The reason for the semi-sweet or bitter-sweet chocolate is two fold - as stated above it is a contrast to the sweetness of the filling, and also this chocolate, with a little grease (butter or shortening) added makes a nice hard topping that crunches went you bite into it.
I have seen other versions of this called New York Slice and Chocolate Custard Bars if that helps anyone! The former usually calls for instant vanilla pudding mix but the TNT Nanaimo uses custard powder (Birds-Eye to be exact).
NBars101 and Jabbur, I hope you enjoy them.