Combine first 5 ingredients, 1/2 cup brown sugar and one teaspoon cinnamon in a large mixing bowl; add buttermilk, butter and eggs. Blend on low speed with an electric mixer until moistened; increase speed to medium and blend 3 more minutes.
Spoon batter into a greased and floured 13"x9" baking pan, set aside. Mix together remaining brown sugar, cinnamon and pecans; sprinkle over batter. Cover and refrigerate overnight.
Bake, uncovered, at 350° for 30 to 40 minutes or until a toothpick inserted in center comes out clean.