Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans.
In a bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Add eggs one at a time, mixing well after each addition.
Stir in vanilla extract.
In another bowl, whisk together the flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture, alternating with buttermilk.
Mix until just combined and smooth.
Divide the batter evenly between the prepared pans.
Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then turn out onto wire racks to cool completely.