Instructions

1. Preheat the oven to 150C/300F/gas mark 2. Grease and line a loaf tin with baking paper. Beat the butter and sugar until light and fluffy. Beat in the zest and eggs with a spoonful of flour to stop it curdling. Sift over the rest of the flour and fold it in with the poppy seeds and the yoghurt.
2. Spoon into the tin and bake for 1 hour, 10 minutes until a skewer inserted into the middle of the cake comes out clean. Cool for 10 minutes in the tin and then turn it out onto a wire rack to cool fully.