Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans with butter or cooking spray. Dust with flour.

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

Cream butter and sugar in a large bowl until light and fluffy, about 3-4 minutes.

Add eggs one at a time, mixing well, then add vanilla extract and mix until smooth.

Alternate adding dry ingredients and sour cream with milk to the mixture, mix until just combined.

Fold in pistachios and white chocolate chips gently.

Divide batter into prepared pans and bake for 25–30 minutes. Check doneness with a toothpick.

Cool in pans for 10 minutes, then transfer to wire racks to cool completely.

Beat softened butter for frosting, gradually add powdered sugar, cream, and vanilla until smooth and fluffy.

Assemble the cake with buttercream between layers and on top, garnished with chopped pistachios.