Hazelnut Cake with Crème Mousseline and Chocolate Buttercream

Hazelnut Cake with Crème Mousseline and Chocolate Buttercream | Sarah Kieffer | The Vanilla Bean Blog
“PHOSPHORESCENCE. Now there’s a word to lift your hat to… to find that phosphorescence, that light within, that’s the genius behind poetry.” – Emily Dickinson

(I apologize for the short post. I’m currently working on my first pass for my book, and don’t have time to talk today. But! I do have this hazelnut cake recipe that I hope makes up for my lack of words. Have a lovely weekend, dear friends.)
Slices of Hazelnut Cake | Sarah Kieffer | The Vanilla Bean Blog

Hazelnut Cake with Crème Mousseline and Chocolate Buttercream | Sarah Kieffer | The Vanilla Bean Blog

Hazelnut Cake Layers on Baking Sheet | Sarah Kieffer | The Vanilla Bean Blog
Hazelnut Cake with Crème Mousseline and Chocolate Buttercream

We made a version of this cake at the Blue Heron Coffeehouse, but used pecans instead of hazelnuts, and an orange filling and frosting. After using hazelnuts in the Dacquoise, I’ve been putting them in everything. The cake layers are very fragile, and since they are made with mostly nuts, they do not have the fluffy texture of a regular cake, there is a bit more ‘chew’ to them. But the cake tastes incredible paired with the mousseline and buttercream.

The cake layer tops will sink in a bit and the cake will pull from the sides as it bakes (see above photo); you may have to cut the layers around the edges to make them all the same size before assembling, or else use tons of frosting to make the cake look straight and even (that’s what I did). But it’s worth it.

The chocolate buttercream in the photos didn’t turn out exactly as I wanted, so I’m instead posting the buttercream from my favorite chocolate cake recipe. But you can use any chocolate buttercream you’d like here.

Hazelnut Cake
2 1/2 cups (290g) hazelnuts, skin on (or you can cheat like I did and buy chopped hazelnuts)
3 tablespoons all purpose flour
4 teaspoons baking powder
3/4 teaspoon salt
6 large eggs
1/4 cup canola oil
1 cup (198g) granulated sugar

Adjust an oven rack to the middle position, and preheat the oven to 350F. Grease two 8 x 2-inch cakes pans, and line the bottoms of the pans with parchment paper.

Place the hazelnuts in a food processor. Process until finely ground.

In a medium bowl, whisk together the hazelnuts, flour, baking powder, and salt.

Put the eggs, sugar, and oil in the food processor and process until combined and smooth. Add the nut mixture, and process again until combined.

Evenly divide the batter between the two prepared pans. Bake until the top is golden brown and springs back when pressed, 22-28 minutes. Move the cakes to a wire rack and let cool for 20 minutes in the pans, then gently invert them and let them finish cooling on the rack.

Crème Mousseline (German Buttercream)
Crème mousseline is basically pastry cream made into a buttercream. I used Ina’s recipe here for the pastry cream, and then followed Joe Pastry’s instructions on how to make the mousseline.

2 cups pastry cream
1 cup (227g) unsalted butter, room temperature and very soft, cut into 1-inch pieces

Place the pastry cream in the bowl of a stand mixer fitted with a whisk attachment. Whisk the pastry cream for a minute, then add the butter pieces one at at time, until incorporated. Keep beating the mixture until smooth and glossy (if your buttercream appears curdled at any point, don’t panic, just keep beating until smooth).

Chocolate Buttercream
6 oz (170g) good semisweet or bittersweet chocolate
1 cup (227g) unsalted butter, room temperature
1 egg yolk, room temperature (you can use 1 tablespoon corn syrup here instead, if you’d rather not use the raw yolk)
1 teaspoon pure vanilla extract
Pinch salt
1 1/4 cups (142g) confectioners’ sugar

Chop the chocolate and place it in a heat-proof bowl set over a pan of simmering water. Stir until just melted and set aside until cooled to room temperature.

In the bowl of an stand mixer fitted with a paddle, beat the butter on medium-high speed until light yellow and fluffy, about 3 minutes. Add the egg yolk, vanilla, and salt and continue beating for 3 minutes. Turn the mixer to low, gradually add the powdered sugar, then beat at medium speed, scraping down the bowl as necessary, until smooth and creamy.

On low speed, add the chocolate to the butter mixture and mix until blended. Use a spatula to finish mixing, making sure the buttercream has no yellow streaks.

To assemble:
Carefully cut each layer of the cake in half horizontally, to make a total of 4 layers (the cake layers are very delicate, so be gentle with them). Put one cake layer cut side up on a turntable or serving plate, and top with about 1/2 cup of the crème mousseline. Use an offset spatula or knife to smooth it out. Repeat with two more layers, and then top the cake with the final layer of cake, cut side down. Frost the top and sides with the chocolate buttercream.
Slice of Hazelnut Cake | Sarah Kieffer | The Vanilla Bean Blog

  • Reply
    Saturday, September 26, 2020 at 5:37 pm

    Hey can u give me the substitute of eggs ??

  • Reply
    Wednesday, September 23, 2020 at 6:24 am

    Amazing cake. Do you know how well it freezes?

  • Reply
    Saturday, March 31, 2018 at 2:59 pm

    I made this cake soon after you originally posted the recipe. It is so good. Delicate and fancy, easy to make. I’m making it again for Easter tomorrow. I made 1 1/2 batches of cake batter so I can make a mini cake also. The Crème mousseline is rich and makes the cake soft and gooey. I will use my favorite chocolate buttercream which is whole eggs no powdered sugar. I used grape seed oil instead of canola and cup for cup instead of regular flour. It’s perfect.

  • Reply
    Tuesday, January 31, 2017 at 3:28 pm

    I recently made this recipe and it was wonderful. The cake was tender, but we loved it. We plan to try the cake again, perhaps with just a bit of powdered sugar, for a non-special occasion dessert.

  • Reply
    robyn holland |
    Friday, May 13, 2016 at 5:28 pm

    cake looks divine. can’t stinking wait for your book. xo

  • Reply
    Wednesday, May 4, 2016 at 5:50 pm

    Would a Vitamix be an okay substitute for the food processor through the whole recipe, or should I just grind the nuts finely and then mix the rest in my KitchenAid? Thanks!! : )

    • Reply
      Friday, May 13, 2016 at 10:27 am

      Erin – So sorry for the late reply! I think the Vitamix should work just fine to finish the recipe. Let me know how it worked for you!

  • Reply
    Abby | Lace & Lilacs
    Saturday, April 30, 2016 at 10:43 am

    These photographs are beautiful, Sarah. I just cannot wait for your lovely book! <3

  • Reply
    Sara @ Cake Over Steak
    Friday, April 29, 2016 at 3:15 pm

    It’s so pretty I can hardly stand it. Also, chocolate + hazelnut is one of my favorite flavor combos of all time.

  • Reply
    Friday, April 29, 2016 at 10:09 am

    This sounds like my kind of cake. Best of luck with your book!

  • Reply
    Kelsey @ Appeasing a Food Geek
    Friday, April 29, 2016 at 9:02 am

    Beautiful! Loving that frosting to cake ratio 😉 Also I can’t wait for the book to drop! Good luck with the final stages! xoxo

  • Reply
    Friday, April 29, 2016 at 5:23 am

    That really is stunning. The colour pairings, the arrangement, everything it’s just a delight. And I looks delicious, too.

  • Reply
    Friday, April 29, 2016 at 4:16 am

    Simply looks heavenly! And the taste combination… Definitely the loveliest cake!

  • Reply
    Thalia @ butter and brioche
    Thursday, April 28, 2016 at 4:14 pm

    isn’t this just the most beautiful cake in the world. love the créme mousseline addition too. and excited for the book! it looks fabulous already.

  • Reply
    Taste of France
    Thursday, April 28, 2016 at 2:42 pm

    This looks amazing. It’s basically Nutella as cake–hazelnut and chocolate. What a match made in heaven.

  • Reply
    Thursday, April 28, 2016 at 1:50 pm

    What a beautiful cake! That icing looks amazing!

  • Reply
    heather (delicious not gorgeous)
    Thursday, April 28, 2016 at 12:13 pm

    pastry cream plus more butter? in the words of ina, how bad could that be? good luck on your first pass!! it looks like you have a great foundation to start from already (:

  • Reply
    Fernando @ Eating With Your Hands
    Thursday, April 28, 2016 at 12:03 pm

    Gorgeous photos on that first pass, congrats!

  • Reply
    Ellie | Hungry by Nature
    Thursday, April 28, 2016 at 12:00 pm

    The amount of frosting on that top layer is making me drool. This is gorgeous! Sending positive vibes your way for your first book pass – good luck!

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