Preheat your oven to 350°F (175°C) and lightly grease a 9x5-inch loaf pan with butter or non-stick cooking spray.
In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, baking powder, baking soda, and salt until they are well combined.
In a separate medium bowl, use an electric mixer on medium speed to beat the softened butter, buttermilk, egg, and vanilla extract until the mixture is smooth and creamy.
Pour the wet ingredients into the dry ingredients and stir with a spatula just until the flour is fully incorporated and no dry streaks remain; be careful not to overmix the batter.
Pour the batter into the prepared loaf pan and spread it into an even layer with the spatula.
Bake for 50 to 60 minutes, or until the top is golden brown and a toothpick inserted into the center of the loaf comes out clean.
Let the bread cool in the pan on a wire rack for 15 minutes before turning it out onto the rack to cool completely.
Notes
Let the bread cool in the pan before turning it out to prevent breaking.