Preheat oven to 160 degrees C. Grease and flour a 12-cup ring tin.
In a large bowl, cream the butter and cream cheese together with an electric mixer until light, about 2 minutes. Gradually at the sugar, beating for another 2 minutes. Add the eggs, one at a time, beating after each until just incorporated.
In a separate bowl, combine the flour and salt. Gradually add the flour mixture to the butter mixture, beating at low speed until just blended. Beat in the vanilla.
Pour the batter into the prepared tin and swirl gently with a knife to remove air pockets. Bake 1 1/2 hours or until a skewer comes out clean. Cool in the pan 15 minutes, then turn out onto a wire rack to let cool completely. Dust with icing sugar.