Line two 25cm round pans with baking paper. Preheat oven to 180 degrees C.
Measure sifted flour, baking powder and salt; sift together three times.
Cream butter or margarine and lemon rind together. Gradually add sugar, creaming until light and fluffy. Add egg yolks one at a time, beating thoroughly after each addition. Add sifted ingredients alternately with milk to the creamed mixture, a small amount at a time; beat after each addition until smooth.