Step 1: Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan or a bundt pan thoroughly.
Step 2: In a large bowl, whisk together the flour, baking powder, baking soda, and salt until well combined.
Step 3: In a separate bowl, beat the eggs and granulated sugar together until the mixture is pale and thick. Gradually pour in the vegetable oil while continuing to whisk.
Step 4: Stir in the orange zest and orange juice into the wet mixture.
Step 5: Gently fold the dry ingredients into the wet ingredients using a spatula until just combined. Do not overmix.
Step 6: Fold in the grated carrots and 3/4 cup of the chopped pistachios.
Step 7: Pour the batter into the prepared pan and bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
Step 8: Allow the cake to cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.
Step 9: For the glaze, whisk the powdered sugar and rose water together until smooth. Drizzle over the cooled cake.
Step 10: Garnish with the remaining pistachios and optional rose petals before serving.