1.Preheat oven to 160°C/325°F. Grease base and side of 24cm (10 inch) round springform tin; line base with baking paper.
2.Sift flours, soda, spices and sugar into large bowl. Stir in walnuts, egg, carrot, banana and oil; pour mixture into tin. Bake about 1¼ hours. Cool cake in tin.
3.Make cream cheese frosting; beat cream cheese and butter in small bowl with electric mixer until as white as possible; gradually beat in icing sugar.
4.Top cold cake with frosting.
You will need about four medium carrots and two large overripe bananas. Use a light vegetable oil, such as canola.