First melt the butter slightly so it's soft enough to whisk. Then combine all ingredients and whisk briskly, or pulse in a blender for 10 seconds. Put the batter in the fridge for at least an hour and up to two days. This allows the batter to settle and reduces the risk of tearing the crepes.
When ready to cook, heat a small non-stick pan to medium heat. Add another tablespoon of butter to coat the pan. Using a measuring cup, scoop out batter 1/8 of a cup per crepe. Pour into the pan and swirl the pan to spread out evenly.
Cook for 30 seconds, then flip, then cook just 10 seconds more before flipping it onto a flat surface to cool. Continue until all batter is gone.