Preheat your oven to 350°F (175°C) and prepare two 9-inch round cake pans by greasing them with unsalted butter and dusting with flour.

In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.

In a large mixing bowl, beat the softened butter and sugar together until light and fluffy.

Add eggs one at a time and mix well. Then add the vanilla extract.

Gradually add the dry ingredients to the wet mixture, alternating with the sour cream and milk.

Fold in chopped pistachios and white chocolate chips gently.

Divide the batter between the prepared pans, smooth the tops, and bake for 25-30 minutes or until a toothpick comes out clean.

Allow cakes to cool in the pans for 10 minutes, then transfer to wire racks to cool completely.

In a bowl, beat softened butter and gradually add powdered sugar, heavy cream, and vanilla extract to make the buttercream.

Place one cooled cake layer on a platter, frost the top, and place the second layer on top. Frost the top and sides of the cake.

Garnish with finely chopped pistachios.