Preheat oven to 180 degrees C. Grease and flour a 25cm ring tin. In a small bowl, beat cream cheese, icing sugar and lemon juice until smooth; set aside. In a medium bowl, stir together flour, baking powder, bicarb soda and salt; set aside.
In a large bowl, cream together the butter and 1 cup white sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Beat in the flour mixture alternately with the sour cream, mixing just until incorporated. Pour half of batter into prepared ring tin. Spoon cream cheese mixture on top of batter to within 1cm of the edge. Spoon remaining batter over filling, spreading to the edge. In a small bowl, combine chopped nuts, 2 tablespoons white sugar and 1/2 teaspoon cinnamon. Sprinkle over batter.
Bake in the preheated oven for 40 minutes, or until a skewer inserted into the centre of the cake comes out clean. Let cool in pan for 10 minutes, then turn out onto a serving plate and serve warm.