In a saucepan, warm the 2 cups of milk with lemon zest (do not boil). Let it infuse and cool to room temperature.
In a large mixing bowl, beat the eggs, sugar, and salt until pale and fluffy.
Add the cooled lemon-infused milk, the extra ½ cup milk, and vegetable oil. Stir to combine.
Gradually fold in the flour until fully incorporated, being careful not to overmix.
Pour the batter into a greased cake pan and bake at 350°F (175°C) for 35–40 minutes, or until golden and a toothpick comes out clean.
Let the cake cool completely before frosting.
To make the frosting, beat mascarpone, powdered sugar, and vanilla extract until smooth. Slowly add heavy cream and beat until light and fluffy.
Spread the frosting evenly over the cooled cake or serve it on the side.