Preheat the oven to 325℉/163℃. Grease and parchment line a 9x13” pan.
Mash the bananas, leaving small chunks, and set aside.
1 ½ cups mashed bananas
In the bowl of a stand mixer fitted with the paddle attachment (or with a handheld mixer), beat together the butter and sugars on medium high speed for 4 minutes, then scrape down the sides of the bowl.
½ cup + 3 tablespoons unsalted butter, ¾ cup light brown sugar, ¾ cup granulated sugar
Add in the eggs one at a time, completely mixing in between, then add the vegetable oil and vanilla. Mix on medium high speed for another three minutes until very fluffy.
3 large eggs, ⅓ cup vegetable oil, 1 tablespoon vanilla paste or extract
Mix together the sour cream and milk. In a separate bowl, whisk together the flour, baking soda, salt, and spices.
3 cups all-purpose flour, 1 ½ teaspoons baking soda, ½ teaspoon kosher salt, 3 teaspoons ground cinnamon, 2 teaspoons ground ginger, 1½ teaspoons ground nutmeg, ½ teaspoon allspice, ½ teaspoon ground cloves, 1 cup sour cream, ½ cup whole milk
Alternate adding flour mixture and milk to the cake batter mixing on low until just combined. Fold in the bananas by hand.
Pour the cake batter into the prepared pan, then bake for 35-45 minutes until set and a toothpick inserted into the center comes out clean.
Note: brown the butter while the cake bakes and transfer to a bowl to re-solidify to room temperature.
Place the cake on a wire rack to cool completely. Do not frost the cake until it is fully cool.