Step 1: Make the Cake

1. Preheat the oven to 350°F (175°C). Grease and flour two 8-inch cake pans.
2. In a bowl, whisk together flour, ground pistachios, baking powder, baking soda, and salt.
3. In another bowl, beat butter and sugar until light and fluffy. Add eggs one at a time, followed by vanilla and almond extract.
4. Alternately add dry ingredients and buttermilk to the butter mixture, mixing just until combined.
5. Divide batter between the pans and bake for 25-30 minutes or until a toothpick inserted comes out clean. Let cool completely.

Step 2: Make the Raspberry Filling

1. In a saucepan, combine raspberries, sugar, and lemon juice. Cook over medium heat until berries break down.
2. Stir in the cornstarch mixture and cook until thickened (about 2 minutes). Let cool.

Step 3: Make the Frosting

1. Beat the heavy cream, mascarpone, powdered sugar, and vanilla until stiff peaks form.

Step 4: Assemble the Cake

1. Place one cake layer on a plate. Spread a layer of raspberry filling on top.
2. Add the second cake layer and cover the entire cake with frosting.
3. Garnish with chopped pistachios, fresh raspberries, and a drizzle of raspberry sauce if desired.
4. Refrigerate for at least 30 minutes before serving.