Cream butter; gradually add 1 cup sugar and ½ cup brown sugar, beating well. Add eggs, one at a time, beating well after each addition. Stir in vanilla. Combine flour, baking powder, soda, salt, and 1 teaspoon cinnamon.
Add to creamed mixture alternately with buttermilk, beginning and ending with flour mixture; mix well after each addition. Pour batter into a greased and floured 13x9 baking pan.
Combine pecans, 1/2 cup brown sugar and 1/2 teaspoon cinnamon; stir well, and sprinkle over batter. Cover and chill 8 to 10 hours or overnight. Uncover batter, and let come to room temperature. Bake at 350 degrees for 35 minutes or until wooden pick inserted in center comes out clean.