Preheat oven to 180 degrees C. Grease and flour a ring tin. In a medium bowl, mix the flour, baking powder and bicarb soda together and set aside. In a separate small bowl, combine 1/2 cup sugar, cinnamon and nuts. Set aside.
In a large bowl, cream butter and 2 cups white sugar until light and fluffy. Add eggs, sour cream and vanilla essence. Add flour mixture and beat until well combined.
Pour half of batter into ring tin. Sprinkle half of the nut mixture on top of batter in pan. Add remaining batter and sprinkle with the last of the nut mixture.
Bake at 180 degrees C for 45 to 60 minutes, or until a toothpick inserted into cake comes out clean.