Preheat your oven to 350°F (175°C) and grease two 9x5-inch loaf pans.

Cream together ½ cup softened butter and 1 cup granulated sugar until light and fluffy.

Add 2 eggs one at a time, mixing well after each addition.

Pour in 1 cup of buttermilk and mix until combined, scraping down the sides.

In another bowl, whisk together 2 cups of flour and 1 teaspoon of baking soda.

Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.

Mix ½ cup brown sugar and 1 tablespoon ground cinnamon in a bowl for the swirl.

Pour half the batter into each loaf pan, sprinkle with cinnamon sugar, and layer with remaining batter and cinnamon mixture.

Bake for 45-50 minutes until a toothpick inserted comes out clean.

Cool in pans for 10 minutes before transferring to a wire rack to cool completely.