Preheat oven to 350°F / 180°C and line two 8 inch cake pans
Cream together the butter and sugar until light and fluffy
Add eggs and beat until combined
Add sour cream and beat until combined
Sift the flour, baking powder, baking soda and salt and add a third of it to the batter, mix in slowly until fully incorporated
Add half the milk and mix in until fully incorporated. Repeat with another third of the flour, the remaining milk, and then the remaining flour
Add the pistachio paste and extracts and stir in until fully incorporated
If you want to add a touch of green colour to the sponge, add a drop of colouring now, though it's beautiful without
Lastly, stir the chopped pistachios into the batter - make these as fine or as chunky as you'd like
Divide the batter between the cake pans and bake for about 45 minutes, or until a skewer inserted comes out clean
Make the Frosting
Once the cake is cooled, start the frosting. Follow my instructions for Italian Meringue Buttercream
Once the frosting is ready, whip in the pistachio paste and almond extract - add more or less according to taste
Fill and Decorate
Level the cakes and cut each cake in half to make four even layers
Stack the layers, filling an even layer of pistachio Italian meringue buttercream in between each one
Cover the entire top and sides in buttercream and decorate how you like, I just used a palette knife to create little waves in the frosting - I like how that looks with Italian meringue buttercream as it's so glossy!