1. Preheat the oven to 350°F (175°C). Grease and flour two 8-inch round cake pans.
2. In a large bowl, cream together the softened butter and sugar until light and fluffy.
3. Add the eggs one at a time, beating well after each addition, then stir in the vanilla extract.
4. In a separate bowl, whisk together the flour, baking powder, baking soda, and ground pistachios.
5. Gradually add the dry ingredients to the wet ingredients, alternating with the milk. Mix until smooth.
6. Divide the batter evenly between the prepared cake pans and bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.
7. Let the cakes cool in the pans for 10 minutes before transferring them to a wire rack to cool completely.

For the Pistachio Cream Filling:

1. In a medium bowl, beat together the heavy cream, mascarpone (or cream cheese), powdered sugar, and pistachio paste until smooth and thickened. Set aside.

For the Whipped Cream Topping:

1. In a chilled bowl, beat the heavy whipping cream with powdered sugar and vanilla extract until stiff peaks form.

Assemble the Cake:

1. Once the cakes have cooled, place one cake layer on a serving platter. Spread the pistachio cream filling over the top.
2. Place the second cake layer on top and gently press down.
3. Frost the top and sides of the cake with the whipped cream topping.
4. Garnish with chopped pistachios or whole pistachios on top, if desired.