I bought a palette knife a few months ago because I was inspired by some painted cakes and decided to try out the technique on this cake I made for my sister’s birthday. I was also loving the watercolor ombre trend and decided to throw that in there too because hey, you only get so many occasions to make a cake.
My sister’s all-time favorite ice cream flavor is ~coffee oreo~ which I really took into stride when planning out the flavors. I wanted to make sure that the aromatic coffee flavor and the nostalgic, crunchy Oreos were both highlighted in this coffee oreo cake. I decided on a rich coffee walnut cake and a simple vanilla swiss meringue buttercream that helped incorporate layers of crumbled Oreos.
I have a love-hate relationship with swiss meringue buttercream but recently won the battle against curdled/soupy/chunky renditions and have listed some of my tips below!
Layer cake process:
The layer cake itself uses instant espresso and coffee extract to hit you with that strong but pleasant coffee flavor. It 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!! I wasn’t sure about what the texture would turn out to be because of the food processor but it came out light and moist.
A Swiss Meringue Aside
Why I love it:
I could write essays on my experience with swiss meringue buttercream (SMB) but I’ll keep it to this for now: it’s life changing. I never thought I would be able to enjoy cake because I always found traditional American buttercream too sweet and rich and 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??
Why I hate(d) it:
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 who recommended blow-drying the bottom of the stand mixer. This gently melted my apparently too cold, but technically room temperature, butter and allowed it to churn together. In conclusion, don’t lose hope on your finicky SMB until you’ve tried hair-drying it!
For the ombre coat, it 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 here for a quick video of my process.
Coffee Oreo Layer Cake
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
- ¼ cup milk
- 1 tbsp instant coffee dissolved in 1 tbsp boiling water
- 1 tsp coffee extract optional but highly recommended
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
Coffee Walnut Layer Cake
- Heat oven to 350 degrees. Butter three 6-inch cake pans, and line base of each with parchment paper.
- In food processor, process walnut pieces and sugar to a fine powder. Add butter, flour, baking powder, salt and eggs. Process to a smooth batter.
- Add milk to coffee mixture and add to batter, process until 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 fully beat in the vanilla and salt, about 30 seconds, until thick and creamy.
- 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.