Preheat the oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan.
In a large mixing bowl, whisk together the flour, sugar, baking soda, baking powder, salt, and cinnamon until well combined.
In another bowl, mix the melted butter, buttermilk, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir gently with a rubber spatula or wooden spoon until just combined. Be careful not to overmix.
Fold in the chopped pecans until evenly distributed throughout the batter.
Pour the batter into the prepared loaf pan and spread it evenly.
Bake in the preheated oven for 55-60 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and let the bread cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
For extra flavor, consider adding a pinch of nutmeg or a teaspoon of orange zest to the batter.
Serve the sweet bread warm or at room temperature.