Zest the lemons, reserving 1 tsp of zest for the topping. Juice 1/4 cup juice from the lemons.
In a large bowl whisk together the olive oil, lemon juice, lemon zest, ricotta, yogurt, vanilla, and egg yolks. Mix well.
Add in the sugar and whisk again.
In a large bowl combine the flour, baking powder, baking soda and salt. Mix well.
Add the flour mixture to the oil mixture and mix until just combined.
Whisk the egg whites to medium-firm peaks. Fold 3/4 of the egg whites into the batter.
Spread the batter into a 9x9 pan, greased and lined with parchment.
Dollop the top of the batter with the remaining egg whites and use a knife to lightly swirl into the batter.
Mix the superfine sugar with the 1 tsp lemon zest and sprinkle evenly over the top of the batter.
Bake at 350 for 40-45 minutes.