Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper and draw two 8-inch circles on the parchment as guides for the dacquoise layers.

In a bowl, combine the finely ground pistachios, powdered sugar, and salt. Set aside.

In a separate mixing bowl, beat the egg whites with an electric mixer until soft peaks form. Gradually add the granulated sugar and continue beating until stiff peaks form and the mixture is glossy.

Gently fold the pistachio mixture into the egg whites in three additions, being careful not to deflate the egg whites.

Divide the mixture evenly between the two prepared circles on the baking sheets. Use a spatula to spread it evenly within the circles.

Bake in the preheated oven for 25-30 minutes, or until the dacquoise layers are lightly golden and firm to the touch. Remove from the oven and let cool completely on the baking sheets.

While the layers cool, prepare the whipped cream. In a mixing bowl, beat the heavy cream, granulated sugar, and vanilla extract until soft peaks form.

Once the dacquoise layers are cool, carefully remove them from the parchment paper. Place one layer on a serving platter and spread half of the whipped cream over it.

Place the second layer on top of the whipped cream and spread the remaining whipped cream on top. Garnish with fresh raspberries or strawberries if desired.

Chill the cake in the refrigerator for at least 1 hour before serving to allow the flavors to meld.