DIRECTIONS Make the cake: preheat oven to 350F (180C). Line a 9-inch square baking pan with parchment paper and set aside.In a bowl mix flour, baking powder, baking soda and salt.In a large mixing bowl, cream butter and sugar and light and creamy. Add eggs, vanilla extract and whisk until combined.Sift in half of the flour mixture and mix and combined. Then, pour half of the buttermilk. Repeat one more time.Add chopped pistachios and fold until combined.Pour the batter into prepared pan and bake for 35-40 minutes or until a toothpick comes out clean.Allow to cool for 5 minutes in the pan, release from the pan and allow to cool completely on a wire rack.Make the frosting: in a bowl beat softened butter, add icing sugar, cream cheese, pistachio paste and beat until smooth.Decorate: when cake is chilled, spread the frosting over the cake. Sprinkle some chopped pistachios.Refrigerate for at least 3 hours before serving.