Tahini Cake

• 1 orange
• 280 gr flour (plain)
• 240 gr tahini
• 200 gr caster sugar
• 180 ml strained orange juice
• 85 gr sultanas
• 60 gr walnuts (finely chopped)
• 14 gr baking powder
• 14 gr ve margarine
• 2 ml bicarbonate of soda