Preheat the oven to 350?F (175?C). Grease and flour a 9-inch round cake pan.

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

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

In another bowl, whisk together the flour, ground pistachios, baking powder, and salt.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Pour the batter into the prepared cake pan and smooth the top.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.

Let the cake cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

In a mixing bowl, beat together the softened butter and powdered sugar until smooth.

Add the milk and vanilla extract, mixing until the frosting is light and fluffy.

Once the cake is completely cooled, spread the frosting evenly over the top.