Step 1: Preheat your oven to 170°C (340°F) and grease and line a 20cm (8 inch) round springform cake tin.
Step 2: In a large bowl, cream the butter and caster sugar together until light and fluffy using an electric mixer.
Step 3: Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next.
Step 4: Fold in the ground pistachios, semolina, flour, baking powder, and salt until just combined.
Step 5: Pour the batter into the prepared tin and bake for 40-45 minutes, or until a skewer inserted into the center comes out clean.
Step 6: While the cake is baking, make the syrup by combining the granulated sugar, water, and lemon juice in a small saucepan. Bring to a simmer for 5 minutes, then remove from heat and stir in the rosewater. Let cool.
Step 7: Once the cake is out of the oven, prick it all over with a skewer and slowly pour the cooled syrup over the hot cake.
Step 8: Allow the cake to cool completely in the tin before removing and garnishing with extra pistachios and rose petals.