1Preheat oven to 300 degrees F (150 degrees C).
Set rack in the middle of the oven.
Butter and flour a 9 1/2 inch springform pan, and tap out excess flour.
2Place the ricotta in a large mixing bowl, and stir it as smooth as possible with a rubber spatula.
Stir the sugar and flour together thoroughly into the ricotta.
3Stir in the eggs 1 at a time to prevent the batter from getting lumpy. Blend in the vanilla, cinnamon, orange zest and salt.
4Pour batter into the prepared pan.
Bake in the center of the oven for about 1 1/4 to 1 1/2 hours, until a light golden color. Make sure the center is fairly firm, and the point of a sharp knife inserted in the center comes out clean.
5Cool on a wire rack. It will sink slightly as it cools. Cover, and chill till serving time.