In a medium saucepan, combine fresh raspberries with sugar over medium heat. Stir frequently for about 10-15 minutes until the mixture thickens and becomes jam-like. Once thickened, remove from heat and mix in a splash of rose water. Allow the raspberry rose jam to cool completely.

In a food processor, blend ground pistachios until finely chopped. In a separate bowl, whisk together plain flour, baking soda, and cardamom, then fold in the pistachio mixture. In another large bowl, combine buttermilk, sugar, eggs, and rose water, beating until smooth. Gradually add the dry mixture to the wet mixture, stirring until just combined.

Preheat your oven to gas mark 5 (190°C) and grease two 7-inch round cake tins. Divide the cake batter evenly between the prepared tins and smooth the tops with a spatula. Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean. Allow the cakes to cool in the tins for 10 minutes before transferring them to a wire rack to cool completely.

In a chilled mixing bowl, pour the double cream and whip it with an electric mixer on medium speed until soft peaks form, about 3-5 minutes. Gently fold in a tablespoon of rose water to infuse the frosting with floral notes. Keep whipping until the frosting holds stiff peaks.

Once the cake layers are completely cooled, place one layer on a serving plate. Spread a generous layer of the raspberry rose jam on top, allowing it to slightly spill over the edges. Place the second layer on top and frost the top and sides of the cake with the whipped rose water cream. Decorate with edible rose petals.