Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a mixing bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy.

Add the eggs one at a time, mixing well after each addition. Stir in the melted white chocolate and vanilla extract.

In another bowl, combine the sifted flour, baking powder, and salt. Gradually add to the wet ingredients, mixing until just combined.

Fold in the chopped pistachios.

Divide the batter evenly between the prepared cake pans.

Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean. Let cool in pans for 10 minutes before transferring to a cooling rack.

In a mixing bowl, beat the softened butter until creamy.

Gradually add the powdered sugar, mixing until smooth.

Stir in the melted white chocolate and heavy cream until well combined. Add vanilla extract and mix until fluffy.

Once the cakes are completely cool, place one layer on a serving plate and spread a layer of frosting on top.

Place the second layer on top and frost the top and sides of the cake.

Garnish with whole pistachios and shaved white chocolate.

Slice and serve the cake.