Preparation time 20 minutes, cooking time 1 hour 20 minutes.
1) Preheat oven to moderately slow. Grease deep 22cm-round cake pan, line base and side with baking paper, extending paper 5cm above edge of pan.
2) Beat butter, rind and sugar in medium bowl with electric mixer until light and fluffy. Add eggs, one at a time, beating until just combined between additions. Fold in flours and juice , in two batches.
3) Pour mixture into prepared pan, bake in moderately slow oven about 1 hour 10 minutes. Stand in pan 10 minutes, turn onto wire rack to cool.
4) Place cake, top-side up, on serving plate, spread cold cake with glace icing.
Place icing sugar is small heatproof bowl, stir in butter and juice. Place bowl over small saucepan of simmering water, stir until icing is of spreadable consistency. Spread over cold cake immediately.
Serve 12, per serving 19.5g fat, 1895kj.