Coffee Hazelnut Cake with Mocha Buttercream

On By neverenoughcounterspaceIn Cakes

When I was little, my birthday always fell during April vacation. I never got to celebrate my birthday at school, and my name never came on over the announcements so that people would know to celebrate me. However, that always meant that I got to go visit my grandmother in New Jersey for my birthday nearly every year, and nearly every year she would make me the best cake in the world. The cake itself I don’t actually remember too well. I think it was usually chocolate. But the real star of the show, the thing I looked forward to all year was her mocha buttercream frosting. It was so silky and creamy and perfect that it has ruined nearly all other frostings for me. 

As I got older and began baking for myself, I asked my grandmother about it. She and my mother, who had made it once and swore never to do so again, said that it was the hardest frosting to make and it nearly always split or went horribly wrong. To protect my own sanity, I therefore chose not to bother trying to make it for many years. However, this year, I really wanted that frosting. I was feeling confident, so I called my grandmother and she sent me a photo of the recipe that she had cut out of the newspaper many years ago:

I was surprised to learn that this recipe, which I had thought of for nearly 20 years as “Omi’s Mocha Buttercream” was actually Julia Child’s! (I’m still going to call it Omi’s). 

Thankfully, the snow missed my birthday by two days this year and I was granted a beautiful, sunny day to atone for last year’s snowstorm. When I thought of what to pair with mocha buttercream, I immediately thought of hazelnuts and I quickly found a recipe for an Italian hazelnut cake called a Torta di Nocciole which I adapted for this recipe. The Italian cake complimented the entire theme of my birthday meal which was the Amalfi Coast (I truly miss being able to travel) and was the perfect ending to a feast that began with freshly baked sourdough bread and focaccia. 

  • Fresh focaccia and sourdough for our antipasto
  • Salad with pistachios, blood orange, and broiled goat cheese
  • Pan seared salmon with lemon and tarragon aioli, fennel, farro risotto, and asparagus

I probably always say this, but I think this really is one of the best cakes I have ever eaten. The hazelnuts taste even nuttier because of the addition of the coffee and it’s not too sweet to contrast with the rich frosting. And the frosting? Well, there is no way to describe it, you just have to try it yourself. 

Recipe: 

For the Cake:

Adapted from this recipe from Food52

Ingredients: 

450 grams raw, shelled hazelnuts 

180 grams plain (all-purpose) flour 

2 3/4 teaspoons baking powder 

225 grams unsalted butter (2 sticks), softened, plus extra for greasing 

100 grams granulated sugar 

7 eggs, separated 

108 milliliters freshly brewed espresso or very dark instant coffee cooled 

225 milliliters whole milk

Method: 

Preheat the oven to 350ºF and grease and line two 8-inch cake pans 

Pulse the hazelnuts in a food processor until the texture of sand. Place in a large bowl with the flour and baking powder.

Separate the eggs. Place the whites into a stand mixer and the yolks into a small bowl. 

Whip the egg whites to stiff peaks and then carefully pour into a large bowl. Be sure not to deflate the whites. 

Put the stand mixer bowl back on the machine (no need to clean it) and beat the butter and sugar together in a stand mixer until creamy and pale.

Add the yolks to the butter and sugar and beat to combine. 

Stir in the dry ingredients, then the cooled espresso and milk, and stir until just combined. Gently fold in the egg whites.

Pour the batter into the prepared tins and bake for 35-40 minutes, or until the top is springy and deep golden brown. Listen to the cakes, if they are still hissing very loudly, they could probably use a couple more minutes. 

Remove from the oven and leave to cool for half an hour, then let the cakes cool on a wire rack completely before frosting. 

For the Frosting: 

Adapted from Julia Child’s buttercream

Ingredients:

1 1/3 cups sugar

1/2 cup water 

2 large eggs 

6 large egg yolks 

1 lb (4 sticks) unsalted butter at room temperature 

2 tsp vanilla extract 

2 tbs instant coffee dissolved in 3 tbs water or an alcohol of your choice (I used 1 tbs Nocello to 2 tbs water) 

Method:

Separate your egg yolks. Place the 6 egg yolks and two whole eggs in the bowl of a stand mixer with the whisk attachment. Beat them until well mixed and no streaks remain. 

Pour sugar and water into a saucepan and boil until the sugar dissolves and the temperature of the sugar reaches 238°F. 

As soon as the sugar reaches that temperature, turn your stand mixer on medium high and slowly stream the sugar into the eggs. Go very slowly because you do not want to curdle the eggs. 

Once you have poured the sugar in, keep the stand mixer on until the egg/sugar mixture is completely cooled. This will take some time. I advise temping the middle of the mixture before adding the butter in the next step. You want the egg mixture and the butter to be the same temperature. 

Once cooled, switch from the whisk attachment to the beater attachment. Add the butter “by gobs,” as Julia says, with the mixer running . Make sure each butter addition is fully incorporated before adding the next. 

Once all the butter is added, pour in the coffee and vanilla. If the buttercream looks grainy or like it is separating at this stage, beat in a little more room temperature butter. 

Assemble the cake and decorate however you wish. I dipped toasted hazelnuts in dark chocolate which was so delicious I made a whole bunch of them to serve on the side!  

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