Preheat oven to 165 degrees C. Grease and flour a 25cm ring tin. Sift into a bowl the flour, bicarbonate of soda and salt. Set aside.
In a large bowl, cream the margarine and sugar until light and fluffy. Beat in the eggs one at a time then stir in the lemon essence. Alternately beat in the flour mixture and the yoghurt, mixing until just incorporated.
Pour mixture into the prepared tin. Bake for 60 minutes or until a skewer inserted into the centre of the cake comes out clean. Allow to cool 10 minutes in the tin before turning out onto a wire rack to cool completely.