"The black and white is more than just a mix-up of vanilla and chocolate."
The gold standard of milkshake flavors typically include chocolate, vanilla, strawberry, and sometimes coffee. But even on the most basic milkshake menu you should be able to request the best flavor of all: the black and white. And if there's malted milk powder behind the counter, even better.
I credit my love of the black and white milkshake to my mother. When the blender came out from under the counter when I was growing up, this was the summer milkshake we made. And later, when she and my stepfather took over a lunch counter in my hometown of Oneida, New York, this was the milkshake she would make me when I was home visiting from college. Their diner, Murphy's Corner, is connected to a working pharmacy, but the vintage soda fountain fixtures are now mostly for show—the calls for milkshakes aren't as popular with their breakfast and lunch crowd.
The ingredients in a black and white are simple: vanilla ice cream, milk, chocolate syrup. Notice that chocolate ice cream doesn't come into the equation here. You'll often find black and whites made with vanilla and chocolate ice cream, but not in my book. The black and white is more than just a mix-up of vanilla and chocolate—it's the way the chocolate syrup introduces an underlying chocolate flavor to the rich vanilla without overpowering it that matters. The result is a creamy concoction that, especially if you add malted milk powder (and you should), introduces a new level of sweetness and nuttiness, reminiscent of Ovaltine.
I've seen more and more shakes billed as "malted" that just include crushed-up Whoppers. While this is fine, and will incorporate an undertone of malty flavor, it's important to really crush them to a chocolate-malty powder, otherwise the chunks just wind up at the bottom of the glass. Another added touch is lining the glass with chocolate syrup, but the syrup should be introduced to the actual mix in addition to being decorative flourish.
Personally, I think topping a milkshake with whipped cream is overkill, but I'll look the other way if you want to add a shot or two of bourbon to the mix when you're making this at home.