Adjust oven rack to center and preheat oven to 350 degrees.
Smear the butter over the bottom and up the sides of an 8 x 3 inch cake pan or springform pan – be thorough and make sure there are no bare spots. Sprinkle a little flour into the pan and rotate to coat sides and bottom; tap out excess.
Whisk together the flour, baking powder, salt and 2 teaspoons of the lemon zest in a bowl.
In a heavy duty mixer fitted with the paddle attachment, beat the eggs for 2 minutes on medium speed. Pour in the olive oil and sugar. Mix on medium-high speed until emulsified.
Lower the speed and add the ricotta cheese. Stir in the flour mixture in two additions.
Scrape batter into prepared cake pan and level the top. Bake 45-50 minutes, or until puffed, golden and a toothpick inserted into the middle emerges clean.
Cool cake in the pan 10 minutes before inverting onto a rack to cool completely.
While the cake cools, blend the butter, mascarpone, powdered sugar, cream and salt in a small bowl until smooth.
Spread the icing over cooled cake and sprinkle the remaining lemon zest over the top.
Notes
The frosted cake will keep in the refrigerator 1-2 days. Wrap the cake (without the icing) and keep at room temperature up to 3 days.