2 cups all-purpose flour
1 cup sugar
1/2 cup firmly packed brown sugar
1 teaspoon baking powder
1/2 teaspoon salt
1 cup buttermilk
2/3 cup melted butter or margarine
2 large eggs

1/2 cup firmly packed brown sugar
1/2 cup chopped pecans, optional
2 teaspoons ground cinnamon

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.

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.