Preheat your oven to 350°F (175°C).
Grease and flour a 9-inch round cake pan.
In a large bowl, cream together the softened butter and sugar until light and fluffy.
Add in the eggs, one at a time, mixing well after each addition.
Stir in the mashed bananas and vanilla extract.
In another bowl, whisk together the flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the banana mixture, alternating with milk, until well combined.
Pour the batter into the prepared cake pan.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.