01 - Preheat oven to 350°F. Grease an 8-inch round cake pan and line with parchment paper.
02 - In a medium bowl, whisk together flour, chopped pistachios, baking powder, baking soda, and salt until well blended.
03 - In a large bowl, rub lemon zest into granulated sugar to release essential oils. Whisk in vegetable oil, eggs, and vanilla extract until smooth and emulsified.
04 - Stir whole milk and fresh lemon juice into the wet mixture until fully incorporated.
05 - Gradually fold dry ingredients into wet mixture, mixing gently until just combined. Take care not to overmix the batter.
06 - Transfer batter to prepared pan, smoothing the surface evenly with an offset spatula.
07 - Bake for 30–35 minutes until a toothpick inserted into the center emerges clean and the cake springs back when touched lightly.
08 - Let cake rest in pan for 10 minutes before turning out onto a wire rack to cool completely.
09 - Beat cold heavy cream in a large chilled bowl until soft peaks form.
10 - Add mascarpone, powdered sugar, and vanilla to the whipped cream. Continue beating until smooth and spreadable, taking care not to overbeat.
11 - Spread mascarpone frosting evenly over the completely cooled cake using an offset spatula.
12 - Sprinkle chopped pistachios and fresh lemon zest over the frosted cake for visual appeal and added texture.