Preheat oven to 350. Lightly grease a 13x9 inch baking pan; set aside.

In a large mixing bowl mix together the brown sugar and flour.

Using a pastry cutter or two knives, cut in the butter until mixture resembles coarse crumbs. Remove 1 cup of mixture and set aside.

To mixture in large bowl add baking powder and salt. Using a fork, lightly beat in vanila, milk and egg.

Continue beating until a smooth batter forms. Pour batter into prepared baking pans.

In a small bowl, combine the chocolate chips and walnuts.

Sprinkle reserved crumb mixture over top of batter in pan. Sprinkle with the chocolate chips and walnuts.

Using a long flat spatula, spread topping evenly over the top of the batter in pan.

Bake bars for 35 minutes, or until a skewer inserted in center comes out clean.

Transfer pan to a wire rack. Cool bars in pan completely before slicing.

Using a serrated knife, cut into 24 bars. Store in an air tight container for up to 5 days.