Cream the butter and sugar together until light and throffy.
Beat in the egg yolks until well mixed.
Add the zest, vanilla and yogurt beating well.
Gently fold in the flour and B.P, until just mixed so as not to overwork the flour.
Meanwhile – beat the egg whites to form soft peaks (merengue)
Fold in the whites, gently trying not to loose the lightness – air.
Spoon in to a greased tray bake tin.
Bake on the middle shelf in a pre-heated oven gas 5 / 170*c for around 35-45 minutes – – until cooked (time depending on depth of tin)
For the syrup
While the cake is baking – make the syrup by boiling and simmering all the ingredients for the syrup together and simmering for 5 minutes to make a slightly thickened stock syrup.
When the cake comes out of the oven – leave in the tin – prick all over with a skewer of fork & pour over the syrup.