Prepare the Cake: Preheat oven to 350°F. Lightly oil a 9-inch round baking pan. Line with parchment paper, and lightly oil parchment. Dust parchment lightly with flour, tapping out excess.
Whisk together flour, cornmeal, baking powder, baking soda, and salt in a large bowl. Whisk together oil, sugar, mascarpone cheese, eggs, lemon zest, and lemon juice in a second large bowl until completely smooth and incorporated. Pour oil mixture into dry ingredients, and stir until evenly moistened and no lumps remain.
Pour batter into prepared baking pan; smooth top. Bake in preheated oven until Cake is golden, has risen, and just starts to pull away from the edge of the pan, about 30 minutes. Cool in pan 30 minutes. Transfer to a wire rack; cool completely, about 1 hour. (Cake can be made, unfrosted, up to 3 days in advance. Store at room temperature tightly wrapped with plastic wrap.)
Prepare the Whipped Mascarpone: Whisk together all Whipped Mascarpone ingredients in a medium bowl until slightly thickened. Spread mixture on Cake.