Preheat the oven to 300 degrees F.
Lightly butter a 9-inch cake pan (preferably a spring form pan).
In a large mixing bowl, combine the ricotta, sugar, candied orange zest, liqueur, orange zest, amaro and 3 egg yolks. Using a wooden spoon, mix until homogenous. Add the egg whites 1 by 1, mixing after each addition.
Pour the ricotta mixture into the prepared pan and bake until light golden brown, about 30 minutes. Serve hot, room temperature or cold.
Recipe courtesy of Mario Batali