Pre-heat oven to 350°F and grease two loaf pans with non-stick cooking spray.
In a medium bowl, whisk together the flour and baking soda; set aside.
In a large bowl, beat together the butter, eggs and 2 cups of sugar until creamy.
Add the buttermilk and dry ingredient mixture; fold in until combined.
In a small bowl, combine the remaining ⅔ cup sugar with the cinnamon; stir to mix.
Spread ¼ of the batter in the bottom of each loaf pan.
Sprinkle ¼ of the sugar mixture over the top of the batter in each pan.
Spread the remaining batter over the top of the sugar mixture in each pan and top with remaining sugar.
Bake in the pre-heated oven for 45 to 50 minutes or until a toothpick inserted in the center comes out clean.
Remove from the oven and allow the bread to cool in the pan until cool enough to touch; then remove from the pan and transfer to a wire cooling rack to cool completely before slicing.
