Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan.
In a mixing bowl, cream together the softened butter and sugar until light and fluffy.
Add the eggs, one at a time, mixing well after each addition.
Stir in the mashed bananas and vanilla extract until well combined.
In a separate bowl, whisk together the flour, baking soda, and salt.
Gradually add the dry ingredients to the banana mixture, alternating with the buttermilk.
Mix until just combined; do not overmix.
Pour the batter into the prepared cake pan.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.