It isn’t even the bowl of the spoon that is used, but rather the back of it.
That’s because its purpose is not to scoop, but rather to break the flow of one liquid being poured into another, so that rather than mixing itself in by the force of the flow, the incoming liquid settles as a layer on top of the other liquid.
They are primarily used for making specialty drinks such as Irish Coffee, “Half and Half” and “Black and Tan.”
The spoons are “held” upside down over the glass or cup. The spoon has a notch in its handle just before the bowl of the spoon, to help it rest on the rim of a glass so that you don’t actually have to hold it, freeing up both your hands. Many have a chain on them for hanging somewhere in your bar.
The name in fact is a bit of a misnomer. You’re not even supposed to pour a liquid onto the back of the spoon’s bowl; you’re supposed rather to “trickle” it slowly. It will take practice to learn the right amount of flow.
Pouring Spoons can also be used when pouring stout on its own, to ensure a perfectly poured glass of stout at home.
Substitutes
A regular table spoon, but you’ll probably have to hold it.