Melt the butter and beat your egg. Once the butter has cooled off a little, mix the two together.
Mix the yoghurt and milk into the egg and butter. Add the vanilla extract. It's all curdled looking, but don't worry, it's fine.
Combine the dry ingredients: flour (ad baking powder if using), salt. Then mix the wet (yoghurt/vanilla/milk and eggs/butter) into the dry and give it a good whisk.
Fold in the mashed bananas just before using.
Heat a heavy bottomed pan until it gets quite hot, and add a large knob of butter. Let it sizzle and froth, then add a ladle's worth for each pancake. Let it sit for a few minutes. You'll see bubbles appearing. Let a few more appear till there are lots - a few minutes on each side should do it - and gently (they are delicate) flip with a fish slice. Give it a few more minutes on the reverse side.
Either serve them as they cook (this is always how it goes down in my house), or keep them all warm and serve together if you are more civilised.
I like a little knob of butter on each one, some more sliced banana and a generous drizzle of maple syrup.