Preheat oven to *375. Combine brown sugar with walnuts & cinnamon, reserve 1/2 cup. Toss remaining mixture with blueberries & set both aside.

Beat butter & sugar at medium speed until light & fluffy. Add eggs one at a time, beating well after each.

Stir together sour cream & vanilla in one bowl, & in another bowl stir together flour, baking powder, baking soda & salt. Add these alternately to batter, starting & ending with flour, beating just until blended.

Spoon half of batter evenly into 24 lightly greased & floured muffin cups. Sprinkle half of berry mixture evenly over batter. Then evenly spread remaining batter over berries & top with remaining berry mixture. Then sprinkle with reserved brown sugar mixture.

Bake at 375 for 20-25 minutes, or until a toothpick inserted in center comes out with only a few moist crumbs. Cool in pans for 10 minutes, then transfer to wire rack too cool completely.