Place the banana in a medium bowl. Smush it with the back of a fork until fully mashed.
Crack the egg into the bowl with the banana. Whisk until well combined.
To the bowl with the banana mixture, add the buttermilk and vanilla. Whisk until well combined.
Add the flour, baking powder, cinnamon, and vanilla. Whisk until just combined - it’ll be a little lumpy because of the texture from the banana.
Heat a medium sized non-stick pan over medium heat. Add a bit of butter to the hot skillet. Once the butter is melted and sizzling gently, scoop ⅓ cup of batter into the skillet. Cook on this side for about 3 minutes – until the edges have set, a few little bubbles are forming on the surface, and the side that is down is golden brown.
Once it's ready, carefully flip the pancake to cook th e second side. Cook about 3 minutes and remove once golden brown. Add more butter if needed, and repeat until you've worked through all the batter.