Preheat the oven to 350°F (175°C) and grease two 9x5 inch loaf pans.
In a large bowl, cream together the butter, sugar, and eggs until smooth.
Alternately mix in the buttermilk, flour, and baking soda until just combined.
Pour half of the batter evenly into the two prepared pans.
Mix together the sugar and cinnamon for the topping and sprinkle half over the batter in the pans.
Add the remaining batter on top and then sprinkle with the remaining cinnamon mixture. Use a knife to swirl the mixture.
Bake for 45-50 minutes or until a toothpick inserted into the center comes out clean.
Allow cooling in the pans for 20 minutes before transferring to a wire rack to cool completely.
