The Black and Tan started as a cocktail. Bartenders would layer a dark beer (typically a stout) on top of a light beer (typically a pale ale or lager) with the help of a spoon. But eventually the cocktail evolved into its own style as breweries began selling the concoction in a single package. Sometimes a final product is greater than the sum of its parts.
While a soup spoon can be use, a designated pouring spoon is the easiest way to make a black and tan at home.
The cocktail works because while dark beer is often “heavier” in flavor, it’s also lighter in gravity, which allows it to float on the lighter beer — an effect that gets partially destroyed as soon as you take a sip. You don’t often get this one in a tap room, though some enterprising breweries like Yuengling, Evil Twin, and Hoppin’ Frog have combined light and dark beers in cans. (They tend to pour black, but with a tan head.)
Warning: do NOT order a Black and Tan in Ireland! The Black and Tans were another name for the violent Royal Irish Constabulary Reserve Force sent by Britain into Ireland in the 1920s, and the drink is considered offensive. If you feel the need for a light beer and a dark beer mixed in a single glass, order a half and half.