First, make the decorations. Roll out the green fondant on a surface dusted with the sugar to a ½cm thickness. Cut out 12 small ‘leaves’ using a cutter or knife. Set aside on some baking parchment. Roll the brown fondant into 12 x 1cm ‘stalks’. Set aside with the leaves.
Heat the oven to 180C/160C fan/gas 4. Line six holes of a 12-hole cupcake tin with red cases, and the other six with green. For the cake batter, beat the butter and both sugars with an electric whisk until light and fluffy. Slowly mix in the eggs, then fold in the flour, baking powder, grated apple and spices until fully incorporated.
Fill the cases three-quarters full and bake for 30-35 mins, or until golden and a skewer inserted into the middle comes out clean. Leave to cool completely in the tin. Meanwhile, make the icing. Beat the butter until light and creamy, then add the sugar and vanilla, and beat for 5 mins more until fluffy and pale.
Spoon the icing into a piping bag fitted with a large round nozzle. Working from the outside towards the centre, pipe the icing in a swirl over the cupcakes, applying a good amount of pressure to the bag. Use a small palette knife to smooth the icing into neat domes, then chill the cupcakes for 30 mins to firm up.
Tip the red and green sanding sugars into separate bowls. Dip the tops of the cupcakes with the red cases into the red sugar, and those with green cases into the green sugar, turning to fully coat the icing.
Make little indentations in the top of the icing for the fondant stalks, and add the leaves around them.