Preheat your oven to 350°F and grease a 9x5-inch loaf pan.

Use a mixer to cream the butter and sugar until light and fluffy. Then add the egg and vanilla to the mixing bowl and mix well.

Combine the flour, baking soda, and salt in a medium bowl. Add half of the dry ingredients to the mixing bowl and half the buttermilk. Mix until just combined. Then add the rest of the flour and buttermilk and mix until combined.

In a small bowl, combine the cinnamon and half a cup of sugar to create the cinnamon-sugar mixture.

Spoon about half of the batter into the prepared loaf pan, using a spatula to level it. Sprinkle two-thirds of the cinnamon-sugar mixture over the batter. Then use a butter knife to swirl the mixture through the batter.

Put the remaining batter on top and use a spatula to smooth it over the cinnamon layer. Sprinkle the rest of the cinnamon mixture on top.

Bake in the preheated oven for 45-50 minutes. When done, it will be golden brown, and a toothpick inserted into the center will come out clean.

Let the loaf of bread cool in the pan for 10 minutes. Then remove it and put it on a wire rack to finish cooling.