Method

• 1.
  Preheat oven to 180°C/160°C fan-forced. Grease two 20cm round cake pans and line base and sides with baking paper. To make the cake, place 125g pistachios, 300g sugar and zest in a food processor and whiz to a reasonably fine meal (it’s okay if there are a few pistachio pieces left; it will look like wet sand). Transfer to a stand mixer fitted with the paddle attachment.
• 2.
  Add butter and beat on medium speed for 8 minutes or until pale and fluffy. Add egg yolks, one at a time, beating well between each addition, then beat for another 5 minutes or until very pale and fluffy. Transfer to a large bowl, then thoroughly wash the mixer bowl.
• 3.
  Place egg whites in the clean bowl of a stand mixer fitted with the whisk attachment and whisk on medium-high speed to soft peaks. Sprinkle over extra 30g sugar and whisk on high speed for 1 minute or until smooth and sugar is starting to dissolve.
• 4.
  Combine flour, baking powder, spices and 1/2 tsp fine salt in a large bowl. Sift half over the pistachio mixture, then stir until almost combined. Stir through half the milk, then repeat with remaining flour mixture and milk. Gently fold through egg whites in 2 batches, being careful not to knock out too much air.
• 5.
  Divide batter between prepared pans. Bake for 10 minutes, then reduce oven to 170°C/150°C fan-forced and bake for another 35-40 minutes until golden and a skewer inserted at the centre comes out clean. Cool in pans for 20 minutes, then carefully transfer to wire racks to cool completely. Wrap cakes in plastic wrap or foil and refrigerate for 3 hours.
• 6.
  For the curd, finely zest one grapefruit, set aside, and peel strips of zest from the remaining grapefruit. Juice both grapefruit (you’ll need 300ml juice; use zested grapefruit from the cake mix if needed).
• 7.
  Place zest strips and juice in a small saucepan over high heat. Boil for 5 minutes or until mixture reduces by one-quarter. Strain into a heatproof jug (you’ll need 1 cup). Whisk sugar and cornflour in a medium heatproof bowl until combined, then add yolks and whisk until pale and creamy. While whisking, slowly add juice mixture until well combined, then pour into a clean medium saucepan.
• 8.
  Bring to a simmer over medium heat, whisking constantly, for 4-5 minutes until mixture is very thick. Whisk in chilled butter, a piece at a time, until well combined. Whisk in 1/4 tsp fine salt, then strain through a sieve into a small container. Discard solids. Cover surface directly with plastic wrap and refrigerate for 1 hour or until soft-set.
• 9.
  For the frosting, place cream cheese and butter in a stand mixer fitted with the paddle attachment. Beat on medium-high speed for 4 minutes or until fully combined and slightly fluffy. Add 50g grapefruit curd, then sift over the icing sugar and 1/4 tsp fine salt. Beat on low speed until sugar is incorporated, then increase to medium-high speed and beat for 3 minutes or until mixture is very thick and silky.
• 10.
  To assemble, level cake tops with a serrated knife. Place one cake, cut-side up, on a plate or cake stand, then spoon 1 cup of frosting on top. Using an offset spatula or the back of a spoon, smooth frosting evenly to the edge, allowing for a little overhang. Spoon 1/2 cup curd on top and spread curd over frosting, leaving a 1cm border all around. Arrange remaining cake cut-side down on top, pressing down gently. Smooth any overhanging frosting into an even edge around the cake (fill any gaps with a little more frosting) then cover the entire cake with a thin layer of frosting and refrigerate for 30 minutes until firmly set.
• 11.
  Spoon remaining frosting on top of the cake and use the back of a dessert spoon to create swirling peaks, then spoon over more curd. Combine the extra 60g chopped pistachio and extra 1/2 tsp cardamom in a small bowl. Sprinkle over the cake, then sprinkle cake with reserved grapefruit zest. Serve cake with any remaining curd alongside and enjoy!