Preheat the oven to 160°C fan / 180°C conventional (355°F). Grease and line two 20cm loose-based round cake tins with non-stick baking paper, then set aside.

In a large mixing bowl, cream together the softened unsalted butter and golden caster sugar using a handheld mixer or a stand mixer fitted with a paddle attachment for about 3-5 minutes, until the mixture is lighter, smoother, and mousse-like. Add vanilla extract and mix again.

Add the eggs one at a time, ensuring that each egg is fully incorporated before adding the next. Continue whisking until the batter is completely smooth.

In a food processor, grind the shelled pistachios into a fine crumb, resembling the texture of ground almonds.

Sift the plain flour and baking powder into the bowl, followed by the fine sea salt and ground pistachios. Carefully fold the mixture until just combined to avoid overmixing.

Divide the batter equally between the two prepared tins, smoothing the top with a spatula.

Bake in the preheated oven for about 35 minutes, or until well-risen and a skewer inserted into the center comes out clean. Allow the cakes to cool in their tins for 15 minutes before transferring to a wire rack to cool completely.

While the cakes cool, prepare the buttercream by creaming together the softened unsalted butter and sifted icing sugar until the mixture is pale and fluffy. Add the smooth pistachio cream, salt, and lemon juice, and mix until well combined. Adjust lemon juice to taste.

Once the cakes are completely cooled, place one layer on a serving plate. Using a piping bag, evenly spread half of the buttercream on top. Spread the raspberry jam in a thin layer over the buttercream, taking care not to let it overflow.

Place the second cake layer on top and generously frost the top with the remaining buttercream. Garnish with fresh raspberries, chopped pistachios, and sprigs of fresh mint for a beautiful finish.