Preheat the oven to 180C/350F/gas mark 4
Use a deep 23cm/9 inch round cake tin.
Grease and line the loaf tin. Cream the butter, vanilla and caster sugar in small bowl until light and fluffy. Add 4 tbs. of sour cream and mix well. Transfer the mixture to large bowl. Stir in the remaining sour cream then the sifted flour and baking powder. Spread half the cake mixture into the prepared tin. Sprinkle with half the combined pecans, brown sugar and cinnamon. Spread evenly with the remaining cake mixture. Sprinkle with the remaining pecan mixture, pressing gently into the cake mixture. Bake for about 1 hour. Stand 5 minutes before turning on to wire rack to cool.
