01 - Preheat the oven to 350°F. Grease and line an 8-inch round cake pan with parchment paper.
02 - In a medium bowl, whisk together flour, chopped pistachios, baking powder, baking soda, and salt.
03 - In a large bowl, rub the lemon zest into the sugar to release oils. Add oil, eggs, and vanilla, whisking until smooth.
04 - Stir in the milk and lemon juice until fully combined.
05 - Gradually fold in the dry ingredients until just incorporated. Do not overmix.
06 - Pour the batter into the prepared pan and smooth the top. Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.
07 - Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.
08 - In a large bowl, beat the cold heavy cream until soft peaks form. Add mascarpone, powdered sugar, and vanilla, and continue to beat until smooth and spreadable. Do not overbeat.
09 - Spread the mascarpone frosting evenly over the cooled cake. Sprinkle with chopped pistachios and lemon zest to garnish.