In a large bowl, combine flour, sugar, baking powder and salt. Cut in butter until mixture resembles coarse crumbs. Stir in walnuts. In a small bowl, beat eggs, milk and vanilla; stir into dry ingredients just until moistened. Gently fold in blueberries. Pour into two 9x5-in. loaf pans. Bake at 350° for 65-75 minutes or until bread tests done. Cool in pan 10 minutes before removing to a wire rack.