Preheat your oven to 350°F (175°C) Line a sheet pan with parchment paper and spread the pistachios in a single layer on the baking sheet. Bake the pistachios for about 8-10 minutes until fragrant.
Keep a close eye on them to prevent burning. They should become fragrant and lightly golden brown when toasted.
Once toasted, allow them to cool completely before pulverizing. If you pulverize them while they are warm, the will turn into a paste. They need to be room temperature. Allow them to cool for 10 minutes.
Once cooled, finely pulverize the pistachios using a food processor to resemble a fine crumb or sand.
Set the blended pistachios aside until you're ready to fold them into the cake batter.
Keep your oven at 350F. Spray a 9×13 metal pan on the bottom, line with parchment paper, and spray again. If you need to use metal binder clips to hold down the sides, remember to use metal, not plastic. Set aside.
In a medium-sized bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until well combined. Set aside.
In a stand size mixer fitted with the paddle attachment, beat the softened butter and granulated sugar together using an electric mixer on medium-high speed until light and fluffy, about 3-4 minutes. With a rubber spatula, scrape down the sides and the bottom of the bowl.
With the mixer on medium high speed, start adding the eggs and egg whites, one at a time, beating for 30 seconds after each addition. Scrape the sides and bottom of the bowl after each addition
With the mixer on low, mix in the sour cream, pure vanilla extract, and almond extract until well combined. It might look slightly clumpy, don’t stress it, once the flour is added it will even out!
Gradually add a 3rd of the dry flour mixture to the wet ingredients, alternating half of with the buttermilk. Mix just until now more flour streaks remain. Repeat this ending with the dry ingredients. Do not overmix.
With a rubber spatula, gently fold in the chopped pistachios until evenly distributed throughout the batter.
Pour the cake batter into the prepared pan and with the back of a spoon spread it out evenly.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out clean or with a few moist crumbs.
Once baked, let the cake cool completely in the pan on a wire rack.
For the lemon curd
I suggest doing this section of the cake a day before to ensure that it sets properly.
In a medium saucepan, whisk the sugar, lemon zest, and lemon juice. in a small bowl, whisk in the whole eggs and yolks until combined, and then whisk them into the lemon mixture.
Whisking constantly, start cooking the mixture over medium-low heat until it’s thick like pudding, about 6 to 8 minutes. It will start to bubble, keep whisking and cook for about 30 more seconds Remove from the heat and whisk in the butter until fully incorporated.
Strain the mixture through a fine-mesh sieve into a small bowl, pushing it through with a rubber spatula. Press plastic wrap directly onto the surface to prevent a skin from forming. Let it come to room temperature and then refrigerate.
For the cream cheese buttercream
In the bowl of an electric mixer, combine the butter and cream cheese. Beat on medium speed for about 2 minutes. Scrape down the sides and bottom of the bowl. Beat again for 2 more minutes.
With the mixer on low, add the powdered sugar, followed by the cream, vanilla extract, and a pinch of salt. Beat on low just until combined. With a rubber spatula, scrape down the sides of the bowl.
Turn the mixer up to medium-high speed and beat for about 3 to 5 minutes.
Assembly
Once the cake has cooled completely in the pan, use a skewer or the back of a wooden spoon to poke holes all over the surface of the cake.
Take the lemon curd and carefully pour or spoon it over the surface of the cake, ensuring that it fills the holes. Use about half of the lemon curd for this step.
Spread the cream cheese evenly over the top of the cake, covering the lemon curd layer.
Take the remaining lemon curd and swirl it onto the cream cheese frosting using a spoon or spatula. You can create a marbled effect by gently dragging the lemon curd through the frosting.
Optionally, you can sprinkle some crushed pistachios or lemon zest on top for garnish.
Once assembled, slice and serve the lemon pistachio cake at room temperature!