Moist apple walnut slice with maple syrup icing

Ingredients

• 3 (450g) apples, peeled, coarsely grated
• 1 cup (150g) potato flour
• 3/4 cup (120g) brown rice flour
• 1/4 cup (30g) ground walnuts
• 1 cup (220g) caster sugar
• 1 teaspoon bicarbonate of soda
• 4 eggs, lightly beaten
• 1 cup (250ml) vegetable oil
• 1/2 cup (55g) coarsely chopped walnuts
• 1 1/2 cup (240g) pure icing sugar
• 1 1/2 tablespoon hot water
• 1 tablespoon maple syrup