Ingredients
4 large ripe bananas, sliced into 1/2-inch rounds
1 (15.25-ounce) box yellow cake mix
3 large eggs
1 cup sour cream (full-fat or light)
1/3 cup dark rum
1/4 cup granulated sugar
1 teaspoon ground cinnamon
1/4 teaspoon salt
2 tablespoons unsalted butter, melted (for greasing and extra richness)
Cooking spray or additional butter for greasing slow cooker
Directions
Lightly grease the inside of a 5- to 6-quart slow cooker with cooking spray or a thin coating of butter, making sure to cover the bottom and about halfway up the sides so the cake releases easily.
Slice the ripe bananas into 1/2-inch rounds and lay them evenly over the bottom of the greased slow cooker in a single, overlapping layer. This banana layer will become the caramelized base of the cake.
In a large mixing bowl, add the yellow cake mix, eggs, sour cream, dark rum, granulated sugar, ground cinnamon, salt, and the melted butter.
Whisk or beat the mixture together by hand or with an electric mixer on low speed just until smooth and no dry cake mix remains. Scrape down the sides of the bowl to make sure everything is fully combined. This is your single, rich batter mixture.
Carefully pour this one mixture evenly over the sliced bananas in the slow cooker, covering all of the fruit. Use a spatula to gently spread the batter so it reaches the edges without disturbing the bananas too much.
Cover the slow cooker with its lid. Cook on LOW for 2 1/2 to 3 1/2 hours, or until the cake is set in the center and a toothpick inserted into the cake portion (not down into the bananas) comes out mostly clean with just a few moist crumbs.
Once cooked, turn off the heat and let the cake rest, covered, for about 10 to 15 minutes. This helps the hot banana layer settle and thicken into a caramel-like sauce underneath.
To serve, scoop down through the cake to the bottom so you get both the soft, cinnamon-rum cake and the caramelized bananas in each spoonful. Serve warm straight from the slow cooker, with ice cream or whipped cream if you like.
Variations & Tips
For a milder flavor, you can replace part or all of the dark rum with milk, half-and-half, or even strong brewed coffee; you’ll still get a cozy, spoonable cake without the alcohol. If you enjoy nuts, sprinkle 1/2 to 3/4 cup chopped pecans or walnuts over the sliced bananas before pouring the batter, for a little crunch and a nod to classic Midwestern nut-topped cakes. A handful of butterscotch or caramel chips scattered over the bananas will melt into an even richer sauce at the bottom. To lean more into warm spice, add a pinch of nutmeg or 1/2 teaspoon of vanilla extract to the batter. If your bananas are extra sweet, you can reduce or omit the added granulated sugar. For smaller households, the recipe halves nicely in a 3- to 4-quart slow cooker; just start checking for doneness around the 2-hour mark. Leftovers reheat well in the microwave—add a spoonful of milk or cream to keep the cake extra moist, much like refreshing an old-fashioned bread pudding.