Preheat your oven to 350 degrees Fahrenheit and prepare two 8-inch cake pans by greasing and flouring them and placing a circle of parchment paper in the bottom of each pan. Set aside.
In the bowl of your stand mixer fitted with the paddle attachment (or in a large bowl with a hand mixer), beat the butter and granulated sugar on medium high speed for a few minutes until fluffy.
Add the eggs one at a time, beating well after each addition.
Beat in the mashed bananas on medium speed, scraping down the sides of the bowl to make sure everything is combined.
Measure out the buttermilk and set it aside.
Measure the flour, baking powder, baking soda, and salt into a separate bowl and add it to the butter mixture on low speed in 3 additions, adding half the buttermilk in between each addition of the dry ingredients.
Mix on low speed just until a batter forms and scrape down the sides of the bowl to ensure everything is incorporated.
Divide the batter between the two prepared pans and smooth out the tops.
Bake at 350 degrees Fahrenheit for anywhere from 24-29 minutes, or until a toothpick inserted into the middle of the cakes comes out clean.
Cool the cakes in their pans for about 10 minutes and then turn them out onto a cooling rack to finish cooling completely.