Make the raspberry filling first, so it has time to cool and thicken.

Place 4 cups frozen or fresh raspberries, 1 cup granulated sugar, 1 tablespoon lemon juice, 2 teaspoon lemon zest, and ¼ cup of water in a saucepan and heat over medium-high heat.

Stir the mixture until it begins to boil. Lower the heat to medium-low, and allow the filling to simmer for 10-15 minutes.

Turn off heat and remove the pot from the stove. Pour the filling into a metal strainer suspended over a medium sized bowl, and push through using a rubber spatula.

In a separate small bowl, make a slurry by combining the remaining 3 tablespoon of water with 3 tablespoon cornstarch.

Add this cornstarch mixture into the strained raspberry filling, and stir until it is incorporated.

Rinse out your pot and pour the filling back into it. Heat at medium heat for a few more minutes, or until the mixture has thickened.

Turn off the heat and pour the raspberry filling into a separate bowl to cool. Cover with plastic wrap and place in the fridge for at least 1 hour, or preferably overnight.

Preheat the oven to 350°F / 175°C. Grease then line three 8-inch cake pans with nonstick spray and parchment paper rounds.

Pour 1 ¼ cups of finely chopped pistachios, 2 cups all-purpose flour, 3 cups granulated sugar, 2 ½ teaspoon baking powder, and 1 teaspoon fine salt into a large bowl or stand mixer. Whisk together until combined.

Mix ¾ cup of room temperature, unsalted butter slowly into the dry ingredients on a low speed.

Pour in 1 cup of egg whites and mix on low until just incorporated.

Mix in 1 ½ cups of sour cream, 2 tablespoon of vegetable oil, 2 teaspoon of vanilla extract, and 1 teaspoon almond extract at low speed until fully incorporated.

Scrape down the sides of the bowl, then beat on medium speed for about a minute.

Divide the batter evenly between the prepared pans.

Bake for 33-36 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.

Let the pans cool for 10 minutes, then run a small offset spatula around the perimeter of the pan.

Place the cake layers into the freezer for 30 minutes to accelerate the cooling process.

Use a serrated knife to level the tops of the layers right before assembling.

If freezing layers, let them thaw for about 20 minutes before making the cake.

Thoroughly clean your mixing bowl before making the raspberry buttercream frosting.

In a medium-sized pot, add about 1 inch of water and bring to a simmer. Add egg whites and granulated sugar into a large metal bowl.

Whisk the mixture constantly until it reaches 160°F/71°C.

Once it reaches this stage, lift the bowl away from the pot and dry the bottom with a towel. Pour the mixture into the bowl of a stand mixer and beat on medium-high speed with a whisk attachment.

Mix for about 10 minutes, or until you have stiff, glossy peaks.

Mix in 2 cups of unsalted butter at medium speed, 1 stick at a time.

Once the consistency is right, swap out the whisk attachment for a paddle attachment and add ¾ cup of the fully cooled raspberry filling, 2 teaspoon vanilla extract, and ½ teaspoon fine salt.

Continue mixing on a low speed for a couple of minutes to make the frosting extra smooth.

Place about 1 cup of buttercream in a large piping bag.

If making in advance, it can sit at room temperature for up to 2 days or stored in the fridge for up to 2 weeks.

Stack and frost the cake layers on a greaseproof cakeboard or flat plate using a dab of frosting.

Spread about 1 cup of raspberry buttercream onto the first cake layer.

Chill the cake in the fridge or freezer until the frosting is firm to the touch.

Spread the remaining raspberry buttercream around the cake and create a textured look.

Add a semicircle of fresh raspberries and chopped pistachios around the top of the cake.