Preheat the oven to 180C (350F).
Melt the butter. Set a side.
Line 7½-8 inch (19-20cm) springform with parchment paper and grease the sides with oil or butter. Set aside.
In a bowl, combine sifted flour, salt, and baking soda. Set aside.
Using a mixer with the whisk attachment, combine eggs and sugar and mix until foamy. Add ricotta cheese, melted butter, vanilla, and the juice and zest of one orange (and orange oil if using). Mix again until incorporated.
To the wet ingredients, add the flour mixture, a little at a time. Mix until just incorporated, but don't overmix.
Transfer to the springform and bake for about 50 minutes (depending on your oven), or until a toothpick comes out clean.
Remove it from the oven and let it cool for a few minutes before removing the springform. After the springform is removed, transfer it to a wire rack to cool completely. You can also leave it overnight in a sealed container and add the frosting the next day.