Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9 inch Bundt pan (can use tube pan).
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the sour cream and vanilla. Combine the flour, baking powder, and salt; stir into the batter just until blended. (If using frozen blueberries, after drying, put some flour in a zip lock bag and shake the berries in that then shake excess flour off of berries). Fold in blueberries.
Spoon half of the batter into the prepared pan. In a small bowl, stir together the brown sugar, cinnamon and pecans (or you can just use a cinnamon sugar mix). Sprinkle half of this mixture over the batter in the pan. Spoon remaining batter over the top, and then sprinkle the remaining pecan mixture over. Use a knife or thin spatula to swirl the sugar layer into the cake.
Bake for 55 to 60 minutes in the preheated oven, or until a knife inserted into the crown of the cake comes out clean, if using frozen berries, bake time is a little longer. (Can try 60 min. in convection oven). Cool in the pan over a wire rack. Don't remove before cool! Invert onto a serving plate, and tap firmly to remove from the pan. Dust with confectioners' sugar just before serving.