Preheat oven to 350 degrees F (175 degrees Celsius).
Whisk together the ricotta cheese, eggs and vanilla in a large bowl.
Stir the lemon zest and the cooled melted butter into the cheese and egg mixture.
In another large bowl stir together the flour, 1 cup granulated sugar, baking powder, and salt.
Use a spatula to fold the flour mixture into the ricotta mixture until thoroughly blended.
Spoon the cake batter evenly into a 9" round cake pan (or a 9" round springform pan) that has been sprayed liberally with baking spray.
Top the cake batter evenly with the fresh blueberries and sprinkle the remaining 2 tablespoons of granulated sugar over the blueberries.
Bake in a preheated oven for 60 minutes, or until a toothpick inserted in the center of the cake comes out clean.
Remove the cake pan to a cooling rack and cool for 30 minutes.
Carefully invert the cake onto a large plate, and then invert the cake once again onto a serving plate so the blueberries are on top. Or, if using a springform pan, run a knife around the edge of the pan to loosen the cake before removing the collar.
Cool the cake completely, and then sprinkle the top with powdered sugar before slicing and serving.
Notes
I don't recommend using frozen blueberries for this recipe because I think they'd bleed too much into the cake batter. Fresh berries will work best for this cake.Store any leftovers, covered well in the refrigerator for up to 5 days.Lemon ricotta cake may be frozen. Store wrapped well, or in airtight freezer containers for up to 2 months. Thaw in the refrigerator overnight.