Place the room-temperature butter, 1 cup sugar and 1/2 cup light brown sugar in the large bowl of an electric mixer and beat until well combined, 2 to 3 minutes. Add the eggs and beat just until the eggs are incorporated. Combine the flour, 1 tablespoon cinnamon, baking powder, soda and salt. Add to batter alternately with the buttermilk. Beat a minute or two at medium-low speed so that the batter is smooth. Lightly flour and oil a 13 x 9-inch baking pan. Pour the batter into pan.
In a small bowl, combine 1/2 cup light brown sugar, pecans and 1/2 teaspoon cinnamon. Scatter this topping evenly over the batter. Dribble the topping with melted butter. Cover the pan with plastic wrap and refrigerate overnight. The next morning, remove the pan from the refrigerator and remove the plastic wrap. If the pan is glass, let it sit at room temperature until the chill is off before putting it into the oven. Bake the coffee cake on the center rack for 30 to 32 minutes at 350°, until the cake springs back in the center when lightly pressed with your finger and a toothpick inserted in the center comes out clean. Remove the pan to a wire rack to cool 15 minutes.