1 (15.25 oz.) box yellow cake mix or pecan cake mix
3 ripe bananas
1/2 cup (1 stick) unsalted butter, melted and slightly cooled
1 teaspoon vanilla extract
Preheat oven to 350º F and lightly grease a 9×5-inch loaf pan with butter or non-stick spray.
Place bananas in a large bowl and mash them until mostly smooth. Stir in melted butter.
Sprinkle cake mix on top of banana mixture and mix until incorporated, then mix in eggs and vanilla extract until smooth.
Pour batter into loaf pan, then place in oven and bake for 45-55 minutes, or until toothpick inserted in center comes out clean.