Using a machine or grater, grate the apple and set aside.
Combine the butter and sugar in the large bowl, using an electric whisk or wooden spoon, beat together until smooth.
Add the egg, little by little and scrape down the sides.
Add the flour, cinnamon, maple syrup, milk and mix together.
Mix in the pecans and apples until combined.
Spoon the mixture into the muffin cases and bake on the middle shelf of the oven preheated to 180C/350F/Gas 4 for 16-18 minutes until risen and golden. Cool on a wire rack.
For the frosting, use a medium bowl and blend half of the cream cheese with all of the butter until smooth. Scrape down the sides, add the icing sugar and maple syrup and mix again. Add the remaining cream cheese and blend until light and fluffy.
Pipe frosting thickly over the cupcakes, decorate with the pecans, lightly dust the nuts with icing sugar, and serve.
Make and decorate the cupcakes up to 1 day ahead and refrigerate in a lidded container.