For the cake, whisk the flour, baking powder, baking soda and salt. Cream the butter and sugar and add eggs one at a time, beating until light and creamy. Add the dry ingredients with yoghurt and vanilla until smooth.
For the topping, combine the sugar, cinnamon and walnuts. Spread half the batter in the prepared tube pan, cover with remaining batter and top with remaining topping.
Bake for approximately 50-60 minutes or until inserted toothpick comes out clean. After 45-50 minutes if it is not done but is becoming too brown cover with foil until baked. Cool and serve.