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