Preheat oven to 200C/180C fan-forced. Line 2 large baking trays with baking paper.
Sift flours and cinnamon into a large bowl. Stir in sugar. Using your fingertips, rub butter into flour mixture until the mixture resembles breadcrumbs. Stir in sultanas and mixed peel. Make a well in the centre. Combine egg and milk in a jug. Pour egg mixture into well. Using a butter knife, mix ingredients to form a sticky dough, adding more milk if necessary.
Spoon 1 ½ tablespoons of mixture, 5cm apart, onto prepared trays.
Bake for 15 to 20 minutes or until golden. Stand for 5 minutes. Transfer to a wire rack to cool. Serve rock cakes warm or at room temperature with butter.
