Zest the limes and squeeze out the juices from 1 1/2 of them and set aside. Separate the eggs then beat the yolks with the sugar until light and creamy. Beat in the flour, then the yoghurt, lime zest and juice. Beat until well mixed.
Whisk the egg whites until stiff peaks form. Gently fold the whites using a metal spoon in a figure of 8 motion into the mixture until combined. Don't over mix as you'll lose the lightness.
Grease a 20-25cm springform baking tin with a little butter then dust with flour, tipping out any excess.Pour in the cake mixture and bake in the oven for 50-60 minutes until brown. The cake will rise magnificently, but then fall back into place when cooling, don't worry yourself, this is supposed to happen. That's it! Let it cool, slightly and remove from the tin to cool completely on a wire rack.
I served mine with a little cream which I'd infused with some rose water that had been sat in my fridge for over 100 years completely unused. It never goes off, apparently.
Video
Notes
TIP: Use either lemons or limes. Use 1 whole lemon or 1 1/2 limes.