Preheat oven to 170 degrees C. Grease and flour one 25cm ring tin.
Cream together the white sugar and 1 cup of the butter. Add the eggs one at time, beating mixture well after each. Mix the bicarb soda with the buttermilk. Add to butter mixture and beat.
Sift flour three times before measuring. Add sifted flour and 1/4 teaspoon salt to the butter mixture. Stir in the 2 teaspoons vanilla. Pour batter into prepared pan.
Bake for one hour. Let cake cool and top with caramel icing.
To make caramel icing: In a saucepan over medium heat cook the brown sugar, remaining 125g butter and the evaporated milk. Stirring frequently bring mixture to a boil and let boil for 3 minutes. Remove from heat and stir in the 1 teaspoon vanilla, beat until thick. Pour over top of cooled bundt cake.