Mash the banana with a potato masher or the back of a fork. (I use a bowl, but you could also do this step in the cup that you'll be serving it in to save time.)
Add the cider and yogurt, and vanilla essence to taste, thoroughly stir with a whisk, and it's done.
I recommend using chilled bananas. Here's "A-jinchan"'s recipe to preserve bananas: https://cookpad.com/en/recipes/168692-how-to-keep-bananas