Preheat oven to 160° C fan forced (180°C conventional)
Grease and Line A loaf tin or 20 cm springform tin
Mix the apple with the lemon juice and lemon myrtle and set aside
Cream the butter and caster sugar with an electric mixer until pale and fluffy
Beat eggs in one at a time until incorporated
Sift flour and fold half through the mixture, then fold in sour cream, then fold the remaining flour
Fold in Apple/Lemon myrtle mixture, including any remaining juice, as well as the mixed spice
Give one final mix on low speed, the mixture should be soft and drop gently off the spoon.
Spoon the mixture into the cake tin, and bake for 50 - 55 minutes, or until a skewer inserted into the middle comes out clean
cool for 15 minutes before removing from cake tin, Place on wire rack to cool, or serve warm if you wish. Best served with custard