Preheat the oven to 350°F (177°C) and grease a metal or glass 9×13-inch pan.

Mash the bananas. I usually just use my mixer for this! Set mashed bananas aside.

Whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.

Using a handheld or stand mixer fitted with a paddle attachment, beat the butter and both sugars on medium-high speed until creamed together, about 3 minutes. Scrape down the sides and bottom of the bowl with a spatula as needed. Add the eggs and the vanilla. Beat on medium-high speed until combined, then beat in the mashed bananas. Scrape down the sides and bottom of the bowl as needed. With the mixer running on low speed, add the dry ingredients in 3 additions, alternating with the buttermilk and mixing each addition just until incorporated. Do not overmix. The batter will be slightly thick and a few lumps are OK.

Spread batter into the prepared pan. Bake for 45–50 minutes. Baking times vary, so keep an eye on yours. The cake is done when a toothpick inserted in the center comes out clean. If you find the top of the cake is browning too quickly in the oven, loosely cover it with aluminum foil.

Remove the cake from the oven and set on a cooling rack. Allow to cool completely. After about 45 minutes, I usually transfer it to the refrigerator to speed things up.

In a large bowl using a handheld or stand mixer fitted with a paddle or whisk attachment, beat the cream cheese and butter together on high speed until smooth and creamy. Add 3 cups confectioners’ sugar, vanilla, and salt. Beat on low speed for 30 seconds, then increase to high speed and beat for 2 minutes. If you want the frosting a little thicker, add the extra 1/4 cup of confectioners sugar (I usually do). Spread the frosting on the cooled cake.

Refrigerate for 30 minutes before serving. This helps sets the frosting and makes cutting easier.

Cover leftover cake tightly and store in the refrigerator for up to 5 days. Bring to room temperature before serving, if desired.