Preheat oven to 350° F. Line two 6-inch cake pans with parchment paper. Lightly butter and set aside.
In a large bowl, whisk together cake flour, baking powder, and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle attachment, cream butter until smooth. Add sugar and mix until incorporated. Add eggs one at a time, mixing on low speed. Make sure each egg in incorporated before adding the next. Follow with two egg yolks and vanilla extract.
Add ⅓ of flour mixture. Mix on low speed until almost combined. Add half of yogurt. Mix until almost combine. Alternate adding flour and yogurt, ending with flour mixture. Mix until there are no longer and streaks of flour.
Divide batter evenly between prepared 6-inch cake pans. Smooth out tops to ensure an even cake surface. Bake for 40-45 minutes until toothpick inserted in center of cake comes out clean. Cool cakes in pan for 10 minutes before inverting onto a wire rack to cool completely.
Combine whiskey and simple syrup. Use to moisten cake during assembly. Moisten cake using a pastry brush.
Whipped Chocolate Ganache Frosting:
Place chopped chocolate in a large bowl.
Bring heavy cream to a simmer. Either place cream in a small sauce pot and heat over medium heat, or alternatively, heat cream in the microwave. Pour hot cream over chocolate. Cover boil with plastic wrap and let sit for 3 minutes.
Remove plastic wrap and stir ganache until homogenous. Cover with plastic wrap (let plastic wrap touch chocolate to prevent condensation formation). Every 30 minutes stir ganache until ganache has thickened to a pipeable consistency.
Place ganache in the bowl of stand mixer. Using a whisk attachment, whip on medium speed until ganache is airy and fluffy.
Slice each cake into two layers so you end up with four layers of yellow cake. Place one layer of cake on a cake stand or cake plate.
If desired, lightly moisten the cake layer with cake syrup using a pastry brush.
Spread about ⅓- ½ cup of whipped ganache atop the first layer. Place another cake layer on top of ganache. Moisten with cake syrup, top with ganache and spread into an even layer. Repeat and continue until you have used all the cake layers.
Spread whipped ganache on the sides of the cake. Smooth the top of the cake and finish by smoothing the sides of the cake with an offset spatula.
Garnish with the cake with fresh berries and chopped pistachios. Keep cake stored in the fridge until ready to serve. Let cake sit at room temperature for at least 15 minutes before serving to allow ganache and cake to soften.
To make simple syrup: bring equal parts water and granulated sugar to a boil. Cook until sugar has dissolved. Cool to room temperature. Keep stored in the fridge until ready to use. Will keep in the fridge for up to a month.