Preheat your oven to 350°F (175°C). Grease the loaf pan or line it with parchment paper.
In a mixing bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon until well combined.
In another large bowl, cream the softened butter and granulated sugar together using a mixer until light and fluffy.
Add in the eggs one at a time, mixing well after each addition. Then mix in the vanilla extract.
Gradually add the dry ingredients to the wet ingredients, alternating with the buttermilk, starting and ending with the flour mixture. Stir until just combined, being careful not to overmix.
Fold in the chopped pecans until evenly distributed throughout the batter.
Pour the batter into the prepared loaf pan and smooth the top.
Sprinkle the additional cinnamon sugar over the top of the batter.
Bake in the preheated oven for 50 minutes or until a toothpick inserted in the center comes out clean.
Remove from the oven and let the bread cool in the pan for about 10 minutes, then transfer to a cooling rack to cool completely.