Banana Oat Cake with Chocolate Buttercream

This is a very simple cake to make. Mixing the batter will only take about 15 minutes and the chocolate buttercream comes together in about 5 minutes.

The cake will also keep well at room temperature for several days so it's a wonderful cake to make in advance. Once frosted with buttercream it should be refrigerated, so if you're preparing it in advance, wait to smear it with chocolate buttercream until the day you plan to serve it.

This recipe will make one 9x13-inch cake, which will give you about 8 slices, depending on how large you cut your slices. And, I'll tell you right now, you're going to want large slices.

Scroll down for information about how to bake this cake as cupcakes or in a round or square pan.

Ingredients needed to make this recipe

• Old fashioned oats: In a pinch, you can use quick cooking oats, but old fashioned give this cake a much better texture.
• All purpose flour and whole wheat flour: All purpose flour keeps this cake soft and fluffy while a bit of whole wheat flour adds flavor and a hearty texture.
• Allspice, baking powder, baking soda, and salt: Everything about the flavor of this cake is warm and comforting and a bit of allspice just dials that up one more notch. Baking powder and baking soda help the cake rise and keep it tender and salt is essential to everything.
• Brown sugar: Brown sugar adds a subtle caramel flavor and keeps the texture of this cake ultra soft and moist.
• Vegetable oil: Because oil doesn't solidify when cool, using oil in this cake instead of butter ensures that it stays soft and tender for several days after baking.
• Vanilla extract & almond extract: You can, of course, use all vanilla and leave the almond extract out of the batter for this cake. But I love using both. Vanilla is essential to bringing out all the other flavors in the cake. Almond extract is one of my secret weapons in baking because it adds another layer of flavor, warmth, and depth.
• 3 large eggs + 1 egg yolk: That extra egg yolk creates an extra rich and tender texture.
• Buttermilk: I use buttermilk in baking a lot because it adds acid to the batter which helps to create a soft, tender, fluffy texture.
• Bananas: Be sure to use very ripe and soft bananas to make this cake. Under ripe bananas are too firm and don't have the same flavor and sweetness that ripe bananas have. Using under ripe bananas will result in a dryer cake with much less banana flavor.
• Heavy cream: After making the batter for this cake, whip some heavy cream then fold it into the batter. This is one of my favorite techniques because that whipped cream adds additional air to the batter, giving cakes a soft, silky texture.
• Classic chocolate buttercream is my favorite frosting choice for this cake. But, I've also listed several other fabulous options below.

Additions and substitutions

The obvious addition to this cake is chocolate chips. I'd suggest using mini chips, which will distribute through the batter better and not interfere with the cake's soft, tender texture. Fold them in at the end of making the batter, along with the whipped cream.

If you love cakes with a nice, nutty crunch, fold in some chopped walnuts or pecans.

If you want to take this cake in a more tropical direction, take a cue from these Hummingbird Cupcakes and frost the cake with cream cheese buttercream topped with a sprinkle of toasted coconut.

• To make a gluten free banana oat cake: Swap out both the all-purpose flour and the whole wheat flour with your favorite gluten free flour blend. My favorite brands are Bob's Red Mill Gluten Free Flour and King Arthur Gluten Free Flour.

Step-by-step photos and instructions

Grease and flour a 9x13-inch rectangle baking pan. (Here's how to grease and flour a pan so your cake will not stick.)

Add ¼ cup of the oats to a food processor and grind to a powder. If, after processing for a minute or two there are still some larger pieces of oats in the bowl, this is ok.

Dump the ground oats and the rest of the whole oats into a large bowl. Add both kinds of flour, the allspice, baking powder, baking soda, salt, and brown sugar. Use a wire whisk to mix the dry ingredients.

Add the oil, vanilla, eggs and egg yolk, buttermilk, and bananas to a food processor or a blender and puree until smooth.

Pour the wet ingredients into the bowl with the dry ingredients. Use a spoon to stir, mixing just until everything is blended together.

Use an electric mixer to beat the heavy cream until it's thick enough to hold a shape. (If you lift the beater from the cream it will form a peak that will hold it's shape.) 

Gently fold the whipped cream into the batter, mixing just until blended - a few visible streaks of cream in the batter is ok.

Spread the batter in the prepared baking dish and bake in the center of the oven for 55-65 minutes. 

Allow the cake to cool completely in the pan then spread with the frosting of your choice.

Pro tip! To test that the cake is done, insert a toothpick in the center of the cake and remove it. If you don't see any raw batter on the toothpick, the cake is ready to be removed from the oven.

So many frosting options!

My favorite frosting for this cake is chocolate buttercream which takes about 5 minutes to make, is super creamy, and intensely flavorful.

But, here are three more delicious chocolate frosting options:

If you opt for chocolate ganache, pour warm ganache over the cooled cake or allow the ganache to cool then use an electric mixer to whip it into a consistency that's similar to buttercream.

And here are four delicious non-chocolate frosting options:

Finally, the coconut cream cheese buttercream on these hummingbird cupcakes would add a delicious tropical touch to this banana oat cake!

Useful equipment and substitutions if you don't have it

This is a super simple batter that comes together in a matter of minutes but there are a few pieces of equipment that make the job even easier.

In this recipe, a food processor is used to grind some of the oats into a powder and to blend the wet ingredients, including the bananas.

If you don't have a food processor, skip the step of grinding some of the oats into a powder and use all whole oats. Mash the bananas with a masher or your hands then use an electric mixer to blend the wet ingredients.

Because the batter for this cake is prepared in a food processor, there's no need for an electric mixer except to whip the heavy cream. I have an electric stand mixer, but for something like whipping a small amount of cream, I prefer to use my handheld mixer.

If you don't have an electric mixer, you can whip the cream by hand, using a wire whisk. This is an excellent arm workout!

This is the food processor and handheld mixer that I own. I love that the food processor has a double blade (genius!). And, when you live in a small space, appliances that multitask are pure gold. This hand held mixer is also an emulsion blender and an electric whisk.

What type of pan is best for this cake?

This recipe is designed to be baked in a rectangle 9x13-inch pan. But, here's how to bake it in different size pans:

• To bake this cake as cupcakes: Divide the batter between two paper lined cupcake pans for 24 cupcake. To make 12 cupcakes, cut the recipe in half (see the pro tip below)
• To bake round layers, use two 8 or 9-inch round cake pans. Be sure to grease and flour the inside of the pans or the cake will stick.
• To bake an 8 or 9-inch square cake either cut the recipe in half (see the pro tip below) or divide the batter between two pans.

Pro tip: To make a smaller cake, cut the recipe in half and bake it in one 8 or 9-inch round or square cake pan. Most of the ingredients are pretty easy to cut in half with the exception of the eggs. Instead of using 3 whole eggs + 1 egg yolk, use 2 whole eggs and omit the extra yolk.

As you can see in the photos above, this is the pan I used to bake this cake. I love this pan. It's lightweight, cooks evenly, and includes a non-stick surface that not only keeps food from sticking but makes washing the pan a piece of cake. 😂

How to store this cake

Unfrosted, this cake will keep well at room temperature for up to 3 days or in the freezer for up to 3 months.

• Cover the cake with plastic wrap to store it at room temperature.
• To freeze, you can leave the cake in the pan and cover it with both a layer of plastic wrap and aluminum foil (if you have a cake pan with a lid, use that). Or, turn the cake out of the pan and wrap it in one or two layers of plastic wrap and then a layer of aluminum foil.

The extra layer of aluminum foil will help prevent freezer burn and prevent the cake from absorbing flavors from the other foods in the freezer.

Once frosted, this cake should be covered and refrigerated after a few hours. A banana oat cake frosted with chocolate buttercream will keep well in the refrigerator for up to 5 days.

More recipes for banana lovers

If you give this recipe a try, let me know! Scroll down to rate this recipe and leave a comment for me.

Happy baking!