Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9 inch round cake pan. 

In a medium bowl, mix together the flour, 1/2 cup of brown sugar, baking powder, baking soda, and salt. In a large bowl, cream together the butter and 1/2 cup of sour cream until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Gradually beat in the flour mixture. Spread half of the batter into the prepared pan. 

In a small bowl, mix together the white sugar, 1/4 cup of brown sugar, and the cinnamon. Sprinkle over the batter in the pan, then sprinkle with the walnuts. Drizzle the caramel topping over the walnuts. Spread the remaining batter over the top. 

Bake for 35 to 40 minutes in the preheated oven, or until a knife inserted into the center of the cake comes out clean. Let cool before serving. Enjoy!