Preheat oven to 180C. Line two trays with baking paper.
Place the almonds, icing sugar and salt in the food processor and blitz until the almonds are finely ground, but not a powder. Add in the butter and continue to blitz until the mixture is well combined. Add in the flour, rose water and vanilla and pulse until everything just comes together, scraping down the bowl as you go if needed. It should be soft but not sticky. Add in more flour if necessary.
Roll the mixture into walnut size balls and arrange on the trays, allowing room for them to spread as they cook. Place the biscuits in the fridge for 10 minutes to firm up slightly. Bake in the preheated oven for around 15 minutes or until just beginning to colour around the edges – they will still be a little soft but will harden on cooling. When cool enough to handle, but still warm, roll the biscuits in icing sugar then allow to cool completely. Dust with extra icing sugar and top with rose petals and pistachios.