Preheat oven to 350 degrees F. Grease well or Butter and flour your bundt pan.
Combine the flour, baking powder, baking soda, and salt.
In a separate bowl, beat the butter and brown sugar until light and fluffy. Beat in the eggs and vanilla.
Mix in the buttermilk and mashed bananas. Slowly add the dry ingredients, stirring gently, just until fully incorporated.
Pour into the prepared bundt pan and bake for 40-45 minutes or until a toothpick inserted comes out clean.
Allow to cool for about 30 minutes before inverting it out of the pan. Frost with cream cheese frosting.
For the cream cheese frosting:
Cream butter and cream cheese together. Add powdered sugar and milk and beat for several minutes, until smooth and fluffy. Add more powdered sugar, if needed.
Store leftover cake covered well at room temperature for 2-3 days or in the refrigerator for up to 1 week.Freeze by wrapping in plastic wrap, then aluminum foil, and freeze for up to 3 months. If the cake is frosted, flash freeze it for 30 minutes to help set the frosting, then cover well. Thaw overnight in the refrigerator, then bring to room temperature before serving, if desired.