1. First, place the ricotta cheese in a bowl with the sugar and whisk until smooth.
2. Add the eggs, one at a time, beating well.
3. Add the cornstarch and baking powder and beat for a few minutes.
4. Then add the zest of the two oranges and the lemon.
5. Add the batter into a round greased with butter pan and bake at 180C or 350F for 45 minutes.
6. When the cake is baked, remove it from the oven and let it cool completely.
7. When cool, cut into slices, sprinkle with powdered sugar and serve.

Adapted from a Recipe by: blog.giallozafferano