Preheat your oven to 300°F (150°C). Line two baking sheets with parchment paper and trace two 7-inch circles on the parchment for uniform layers.

Beat 5 large egg whites until soft peaks form, then gradually add ⅝ cup granulated sugar, 1 tsp cream of tartar, and ¼ tsp salt until stiff peaks are achieved.

Gently fold in 1¼ cups finely ground pistachios, ½ cup powdered sugar, and ⅓ cup cake flour into the meringue using a rubber spatula.

Transfer the meringue into a piping bag and pipe inside the traced circles. Bake for 30-35 minutes or until dry to the touch.

Prepare sugar syrup by combining ¾ cup granulated sugar and ⅓ cup water in a saucepan. Bring to a gentle boil until it reaches 240°F (115°C).

Whisk 8 large egg yolks until pale, then slowly pour in the hot sugar syrup while whisking continuously. Mix in 2½ sticks of unsalted butter and 4 tbsp of pistachio paste until smooth.

Once meringue layers have cooled, assemble the cake by spreading buttercream between layers and on top.

Chill the cake in the refrigerator for at least 1 hour before serving. Let sit at room temperature for 30 minutes before slicing.