Preheat your oven to 350°F (175°C). Grease a 9x5-inch loaf pan and set aside.
In a large mixing bowl, combine the flour, brown sugar, baking powder, baking soda, and salt. Whisk together until well mixed.
In another bowl, cream the softened butter with the brown sugar until light and fluffy. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the wet mixture, alternating with the buttermilk. Start and end with the dry ingredients, mixing until just combined. Do not overmix.
Pour the batter into the prepared loaf pan and smooth the top. Bake for 50-60 minutes, or until a toothpick inserted into the center comes out clean.
Allow the bread to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.