Preheat oven to 350°F (175°C). In a food processor, pulse shelled unsalted pistachios until finely ground. Combine ground pistachios, sifted all-purpose flour, baking powder, and salt in a mixing bowl. Whisk until evenly mixed.

In another large bowl, beat softened unsalted butter and granulated sugar together until light and fluffy, about 3-5 minutes. Add large eggs one at a time, mixing well after each addition. Pour in whole milk, vegetable oil, vanilla extract, and almond extract, mixing until smooth.

Gently fold dry ingredients into wet mixture using a spatula. Avoid overmixing to maintain a light batter.

Divide batter among three greased and lined 8-inch round cake pans. Bake for 22-25 minutes, or until a toothpick comes out clean.

Allow cakes to cool in pans for 10 minutes, then transfer to a wire rack to cool completely.

In a chilled bowl, whip heavy cream until soft peaks form. Add cold mascarpone cheese and powdered sugar, folding until smooth and creamy.

On a serving plate, layer the cooled cakes, spreading mascarpone frosting between layers and over the cake's exterior for a smooth finish.

Refrigerate the assembled cake for at least 2 hours before serving. Garnish with chopped pistachios and optional decorations just before serving.