CAKE
Preheat the oven to 350°F (180°C), placing the rack in the middle position. Line a 9-inch-diameter (23 cm) springform pan with parchment paper.
In a bowl, using an electric mixer, beat the butter and sugar until a creamy, pale-yellow mixture forms.
Blend in the eggs, one at a time, and add the rose water with the last egg.
Continue beating until the mixture has doubled in volume.
Add the yogourt, blending gently.
In another bowl, sift together the dry ingredients.
Gradually add them to the egg mixture, beating on low speed until a smooth batter forms.
Add the pistachios and mix gently.
Pour the batter into the pan and lightly tap the pan on the counter to remove air bubbles.
Bake in the oven for 35 to 45 minutes or until a toothpick inserted in the centre of the cake comes out clean.
Let the cake cool completely on a wire rack.
ASSEMBLY
To serve, top the cooled cake with the yogourt. Sprinkle with pistachios and rose petals.
The cake will keep for up to 2 days in an airtight container at room temperature, or up to 1 month in the freezer in a sealable freezer bag.