Add all the ingredients except the melted butter to a blender. Blend until very smooth, 1-2 minutes.
Pour into a jug, cover and rest in the fridge for about 20 minutes. You can also do this overnight. I recommend not missing this step out - as the batter rests air bubbles rise to the top giving you a smoother batter.
Once you are ready to make your pancakes heat a large frying pan on medium heat and add a small knob of the butter. As it melts tilt the pan to evenly coat the bottom of the pan (do this for each pancake). Pour in some batter and tilt the pan again to form a thin pancake.