Combine first 6 ingredients in a large mixing bowl; add buttermilk, butter, and eggs. Beat at low speed with an electric mixer until moistened; beat at medium speed 3 minutes. Spoon batter into a greased and floured 13x9x2 pan. Combine 1/2 cup brown sugar, pecans, and 2 teaspoons cinnamon; sprinkle over batter. Cover and refrigerate 8 to 12 hours. Uncover and bake at 350 degrees for 30 to 35 minutes or until a wooden toothpick inserted in center comes out clean. Serve warm. Yield: 12 to 15 servings.
Note: Overnight Coffee Cake may be baked immediately at 350 degrees for 30 minutes. To reheat, cover with aluminum foil, and bake at 350 degrees for 5 minutes or until heated thoroughly.