Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan with butter or non-stick cooking spray and set it aside.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt until they are well combined.
In a large bowl, use an electric mixer on medium speed to cream the softened butter and sugar together for 2-3 minutes, until the mixture is light and fluffy. Beat in the egg and vanilla extract until just combined.
Using a spatula, gently fold half of the dry ingredients into the butter mixture, followed by all of the sour cream. Fold in the remaining dry ingredients until a few streaks of flour remain, then carefully fold in the blueberries until the batter is just combined; do not overmix.
Pour the batter into the prepared loaf pan and spread it into an even layer. Bake for 55-65 minutes, or until a toothpick inserted into the center of the loaf comes out clean.
Let the loaf cool in the pan on a wire rack for 15 minutes. Then, carefully turn it out of the pan onto the rack to cool completely before slicing.
Notes
Let the loaf cool completely before slicing for cleaner cuts.