Arguably the best flavor combination ever, coffee and oreo take front and center in this fun watercolor cake! Try out this elegant coffee walnut layer cake with Oreos and rich vanilla Swiss meringue buttercream.
When making this cake for my older sister’s birthday, I drew inspiration from her favorite ice cream flavor: coffee Oreo. Think fragrant espresso ice cream studded with dark cocoa cookie pieces. Elegant, yet with a hint of childhood nostalgia. It doesn’t get much better than that!
Translated into cake flavors, the iconic coffee oreo ice cream turned into a rich coffee walnut cake layered with crumbled Oreos. And to top it all off, a simple vanilla Swiss meringue buttercream that helps to mellow all the flavors out.
Needless to say, it was an immense crowd-pleaser and I am so excited to share this recipe with you!
Let’s Make A Coffee Oreo Layer Cake
Coffee Walnut Cake
The layer cake itself uses instant espresso to hit you with that strong but pleasant coffee flavor. Although optional, I would highly recommend adding in coffee extract to deepen that flavor. This recipe also incorporates a quick walnut flour which adds another degree of nuttiness. The best part? The whole batter can be made in a medium food processor which simplifies prep and cleanup!
Make the Batter
Heat oven to 350ºF . Butter three 6-inch cake pans and line base of each with parchment paper. In a food processor, process walnut pieces and sugar to a fine powder. Add butter, flour, baking powder, salt, eggs, and optional coffee extract. Process to a smooth batter.
Add milk to the instant coffee dissolved in 1 tbsp boiling water mixture and add that to the batter. Process until just combined. Scrape down food processor if necessary. Batter should be thick but not dry, add milk if necessary.
Bake the Layers
Bake until risen and a toothpick inserted comes out clean, about 25 minutes. Cool on a rack for 10 minutes, then remove from pan and cool completely. Level cakes if domed.
Vanilla Swiss Meringue Buttercream (SMB)
Saying that my journey with SMB has been tumultuous would be an understatement. However, the reward is so great when you get it right that it makes it all worth it. I never thought I would be able to enjoy cake fully because all I knew was traditional American buttercream. Normal buttercream was absolutely too sweet and rich and I was almost repulsed at the notion of using it in my own baking.
But this!! SMB!! Most of its mass is made of *cooked* egg whites instead of just butter and sugar, which allows the buttercream to be much lighter. And, unlike traditional buttercream, you can significantly decrease the amount of sugar without affecting the flavor. But that’s not to say it was an easy path to get here – it took multiple trials, some trashed batches (aka many regrets), and a lot of… hair drying??
Swiss Meringue Buttercream Troubleshooting
Hit my line if you want to talk egg white peaks or sugar dissolving, but the problem I kept on running into was my frosting looking curdled after adding in butter. From the pros on the internet, I tried using a double boiler (terrible), chilling overnight (???), and whipping until I felt the weariness of my stand mixer in my soul.
I finally came across a genius comment on a Youtube video that recommended blow-drying the bottom of the stand mixer. I found that the problem was that my butter was separating instead of creaming. Blow-drying the bowl of the stand mixer gently melted my apparently too cold, but technically room temperature, butter. This allowed the butter to churn together without turning into a puddle. In conclusion, don’t lose hope in your finicky SMB until you’ve tried hair-drying it!
But hopefully you’ll have better luck than me, so this is how you make Swiss meringue buttercream!
For more details and troubleshooting, check out my Best Swiss Meringue Buttercream post that makes it so easy!
Swiss Meringue Buttercream Step-by-Step
In a dry, grease-free, heatproof mixing bowl, whisk together egg whites and sugar. Set bowl over a double boiler (saucepan filled with a few inches of simmering water) over medium heat. Make sure that the bowl does not touch the water. Whisk the whites and sugar constantly until sugar is dissolved and mixture has thinned out, or until mixture reaches 160°F, about 4 minutes.
When the mixture is still warm, transfer to the bowl of stand mixer fitted with a whisk attachment. On high speed, beat the mixture until stiff glossy peaks form and the meringue is no longer warm to the touch, at least 10-15 minutes. If it still feels warm, wait until room temperature before adding butter.
On medium-high speed, add the butter 1 tablespoon at a time. Wait for the butter to fully mix in before adding the next tablespoon. After all the butter has been added, turn the mixer down to medium speed and fully beat in the vanilla and salt, about 30 seconds, until thick and creamy. If you want to troubleshoot your SMB, I recommend Sally’s post which has a ton of additional tips!
At this point, you can add in a few drops of gel food coloring depending on how you want to decorate your cake.
Decorating the Coffee Oreo Cake
I’m always down to experiment with different cake decorating techniques. This time, I opted for my first ombré style cake!
Ombré Cake Decorating
The method was a matter of applying swatches of blue, purple, and pink-tinted buttercream and smoothing it out with an offset spatula or cake smoother. It took several reapplications to get a smooth coat so don’t be afraid to layer it on! For the painted flowers, I used a palette knife and a few small paint brushes to paint 3 variations of the same pattern of a flower chain. Finally, I dotted with gold pearl sprinkles which added some more dimensions to the cake! You can check out my Instagram post for a quick video of my process.
Even without a whole lot of decoration, the coffee and oreo flavors speak for themselves. Try this cake for your next occasion, big or small!
If you’re looking for more cake inspiration, check out my Black Sesame Layer Cake or my Chocolate Earl Grey Cheesecake Cake!
Coffee Oreo Layer Cake
Ingredients
Coffee Walnut Layer Cake
- butter for pans
- ½ cup walnut pieces
- 1 cup sugar
- 2 sticks butter, room temperature
- 1 ⅔ cup flour
- 1 tbsp baking powder
- ½ tsp salt
- 4 eggs, large
- 1 tsp coffee extract optional but highly recommended
- ¼ cup milk
- 1 tbsp instant coffee dissolved in 1 tbsp boiling water
Vanilla Swiss Meringue Buttercream
- 4 large egg whites 180 grams
- 1 cup granulated sugar less if desired
- 1⅛ cups unsalted butter, softened but at room temperature 2¼ sticks; 263 grams
- 1 tsp vanilla extract
- ⅛ tsp salt
Decorating and Assembly
- 10 oreos, more as needed
- food coloring, as needed
Instructions
Coffee Walnut Layer Cake
- Heat oven to 350°F. Butter three 6-inch cake pans and line base of each with parchment paper.
- In a food processor, process walnut pieces and sugar to a fine powder. Add butter, flour, baking powder, salt, eggs, and optional coffee extract. Process to a smooth batter.
- Add milk to the instant coffee dissolved in 1 tbsp boiling water mixture and add that to the batter. Process until just combined. Scrape down food processor if necessary. Batter should be thick but not dry, add milk if necessary.
- Bake until risen and a toothpick inserted comes out clean, about 25 minutes. Cool on a rack for 10 minutes, then remove from pan and cool completely. Level cakes if domed.
Vanilla Swiss Meringue Buttercream
- In a dry, grease-free, heatproof mixing bowl, whisk together egg whites and sugar. Set bowl over a double boiler (saucepan filled with a few inches of simmering water) over medium heat. Make sure that the bowl does not touch the water. Whisk the whites and sugar constantly until sugar is dissolved and mixture has thinned out, or until mixture reaches 160°F, about 4 minutes.
- When the mixture is still warm, transfer to the bowl of stand mixer fitted with a whisk attachment. On high speed, beat the mixture until stiff glossy peaks form and the meringue is no longer warm to the touch, at least 10-15 minutes. If it still feels warm, wait until room temperature before adding butter.
- On medium-high speed, add the butter 1 tablespoon at a time. Wait for the butter to fully mix in before adding the next tablespoon. After all the butter has been added, turn the mixer down to medium speed and beat until thick and creamy, around 2-4 minutes more. Finally, fully beat in the vanilla and pinch of salt, about 30 seconds.
Assembly
- Starting with one of the cake layers, smooth on buttercream in a uniform layer. Crumble oreos and sprinkle on top of buttercream. Repeat with remaining cake layers, making sure that the topmost layer is facing downwards (to ensure a smooth top).
- Apply a crumb coat of buttercream. Chill, and decorate as desired.