Using a held-held beater, cream together the butter and icing sugar until pale and fluffy. Add flour, spices and salt and mix through until a firm dough is formed.
Roll out dough until 1.5cm thick and slice into rectangles. Place on a tray lined with baking paper and chill in the fridge for 30 minutes.
Preheat oven to 180°c fan bake.
When dough has chilled, bake for approximately 15 minutes or until golden. Remove from oven and allow to cool completely.
For the marshmallow, add boiling water and gelatine to a large bowl, stirring to dissolve. Add sugar, rose water and colouring, and beat with a hand-held beater on high for 10 minutes until thick, fluffy and sugar has dissolved.
Pipe on top of cooled shortbread and sprinkle with dried rose petals.