Preheat oven to 350 degrees F. Grease and flour a 9 inch (10-cup) Bundt pan.

In a large bowl, beat the butter and sugar until light and fluffy, about 2-3 minutes.

Add the eggs one at a time, beating well between each addition. Scrape down the bottom and sides of the bowl, then add in the sour cream and vanilla mixing until combined.

Add the flour, baking powder, and salt, mixing them into the batter just until blended in.

Gently fold in blueberries. If using frozen blueberries, no need to thaw. Just toss them with 1 tablespoon of flour first. The batter will be thick.

Generously spray a 10- or 12-cup bundt pan with baking spray or grease well with butter and dust with flour. Spoon half of the batter into the prepared pan.

In a separate bowl, stir together the brown sugar, cinnamon and chopped walnuts. Sprinkle the brown sugar mixture over the batter in the pan.

Spoon the remaining batter on top of the brown sugar walnut layer, and smooth it out.

Bake for 55 to 70 minutes until a knife or long skewer inserted into the cake comes out clean with just a few crumbs.

Cool in the pan for 10 minutes, hen invert the bundt pan onto a cake plate or other serving plate. The cake should come right out, but if not, tap the pan firmly a few times with the butt end of a knife to help loosen it. Let cool, then dust with powdered sugar just before serving. I like to serve this cake slightly warm, but it's delicious completely cooled as well.