320 deg F (160 C)

Line a split form 20cm cake tin.

In a large bowl whisk the yogurt, eggs, vegetable oil, sugar, and the zest and juice of 1 lemon.
Sift in the flour, baking powder and a pinch of salt, then mix until just combined.

Bake for 1 hr until a skewer comes out clean.
Cool in pan for 5 mins.
Transfer to a wire rack to cool completly.

Use a electric whisk and beat butter until soft. Mix in the icing sugar a third at a time, followed by 4 Tbs. lemon juice. Whisk until the mixture is fluffy and smooth.

Ice cake and decorate with sugared lemon slices.