Heat oven to 160C/fan 140C/gas 3. For the cake, finely grate the zest from the orange and squeeze 3 tbsp of juice. Pour the juice over the raisins in a bowl, stir in zest, then leave to soak while you make the cake. Lightly oil and line the base of a deep 20cm square cake tin. Mix the flours with 1 tsp baking powder, bicarbonate of soda and cinnamon.
Separate one of the eggs. Put the white in a small bowl and the yolk in a large one. Break the remaining whole egg in with the yolk, then tip in the sugar. Whisk together for 1-2 mins until thick and foamy. Slowly pour in the oil and continue to whisk on a low speed until well mixed. Tip in the flour mix, half at a time, and gently stir it into the egg mixture with a rubber spatula or big spoon. The mix will be quite stiff. Put the extra pinch of baking powder in with the egg white and whisk to soft peaks.
Fold the carrot, raisins (and any liquid) into the flour mixture. Gently fold in the whisked egg white, then pour into the tin. Jiggle the tin to level the mixture. Bake for 1 hr until risen and firm or until a skewer inserted in the centre comes out clean. Leave to cool in the tin 5 mins, turn out onto a wire rack, peel off the paper, then leave until cold.
To make the frosting, stir the soft cheese, Quark, icing sugar and orange zest together - don't overbeat. Stir in the lemon juice. Swirl the frosting over the cake and cut into 16 square. This cake is even better if left well wrapped for a day or two before icing and eating. Will keep up to 5 days uniced in an airtight tin, or in the fridge if iced.