1-Preheat the oven to 355°F (180°C/160°C fan): Preheat the oven to 355°F (180°C/160°C fan) and grease and line 2 x 8-inch (20 cm) loose-bottomed round cake pans with parchment paper. Set aside.
2-In a large bowl with a handheld: In a large bowl with a handheld or stand mixer fitted with the paddle attachment, cream together the butter and sugar for about 3-5 minutes – or until the mixture is lighter in color, completely smooth, and mousse-like. Add the vanilla extract and mix again.
3-Add the eggs, one at a time,: Add the eggs, one at a time, whisking until the batter is completely smooth.
4-In a food processor or blender, grind: In a food processor or blender, grind the pistachios into a fine crumb, like the texture of ground almonds/almond meal.
5-Sift in the flour and baking powder: Sift in the flour and baking powder before adding the salt and ground pistachios. Fold in carefully until just combined.
6-Divide the batter equally between the two: Divide the batter equally between the two prepared pans, then smooth over the surface with a spatula or the back of a spoon to flatten into an even layer.
7-Bake for about 35 minutes – or: Bake for about 35 minutes – or until well risen and a skewer inserted into the center comes out clean. Remove from the oven and leave to cool in the pans for 15 minutes before turning out onto a wire rack to finish cooling completely (the green color on the outside might fade slightly; don’t worry – it will still be vibrant inside).
8-Meanwhile, prepare the buttercream: Meanwhile, prepare the buttercream: In a large bowl with a handheld or stand mixer fitted with the paddle attachment, cream together the butter and sifted confectioners’ (icing) sugar until pale and increased in size. Add the pistachio cream, salt, and lemon juice, and beat again. Taste and adjust the lemon, as needed.
9-Once the cakes have completely cooled, set: Once the cakes have completely cooled, set one on a flat plate. Spoon the buttercream into a piping bag and pipe half the buttercream on top in an even layer. Use a palette knife to spread the jam on top in a smooth and even layer – take care not to go too near the edges, or it will pour out the sides (although you do want to be able to see it). Top with the second cake, followed by the remaining buttercream.
10-Decorate with fresh raspberries, sprigs of fresh: Decorate with fresh raspberries, sprigs of fresh mint, and chopped pistachios. Enjoy!