Chocolate Chestnut Cake

This rich and fudgy chocolate chestnut cake features four layers of moist chocolate cake. Chestnuts add a nutty twist to the decadent chocolate mousse filling. It's topped with a layer of dark chocolate ganache.

The cake batter is easy to make by hand. It's baked in a half-sheet pan, generously spread with mousse, and assembled into a rectangular four layer stack.

This chocolate layer cake is a dramatic centerpiece for any special occasion and is sure to impress. If you're a chocolate lover, don't pass this one up!

The origins of this chestnut chocolate mousse cake recipe trace back to when I was a student in college studying abroad for a year in Seville, Spain. It was there I met my Spanish husband. We lived there together for several years before we eventually moved back to the US. I have fond memories of winter holidays in southern Spain.

Come December, we loved to walk the city streets most evenings, window shopping the beautiful storefront displays, admiring the twinkling lights stretched between buildings like banners, people watching, and enjoying the hustle and bustle of activity.

Chestnut roasters would station their carts piled with hot coals and chestnut bags on the street corners. We could see (and smell) them from afar through the wafts of smoke emanating from their fires.

We'd buy a newspaper cone of castañas so irresistibly piping hot that we'd curse and blow on our soot smudged fingers while trying to peel the outer shells apart. It's an indelible memory of mine, one that I'll always associate with December in the south of Spain.

With that picture in mind, I began brainstorming chestnut dessert recipes, and landed upon a chestnut chocolate cake combination. I wanted to see if I could adapt my chocolate olive oil bundt cake into a flatter, half sheet pan version that I could cut and layer into a rectangular shape. I had success after adjusting the temperature and process to ensure a uniformly flat cake without doming.

For the filling, I first tried making a chocolate chestnut buttercream. It spread on like a dream, but after a few hours, was disappointingly dense, like mortar between the layers of moist chocolate cake. When I went back to the drawing board, I imagined an airy, lighter filling.

I ended up using this excellent recipe for chocolate chestnut mousse from Anna Stockwell on Epicurious, minimally adapting it to include smoked sea salt in homage to the roasted chestnuts from the street vendors in Spain.

This chestnut chocolate mousse cake might now be the cake of my dreams. Topped with a smooth dark chocolate ganache, it's beautiful to look at, slices into dramatic layers, and is even more decadent to eat. The dark, fudgy flavor of the cake perfectly compliments the nutty creaminess of the velvety mousse.

Ingredients

* See recipe card for full list of ingredients and quantities.

For the chocolate cake

All purpose flour - provides structure to the cake. Feel free to substitute with a cup for cup style gluten free flour if desired.

Rye flour - Replacing part of the all purpose flour with rye flour imparts a more complex, nutty flavor to this chocolate cake, which enhances the chestnut notes in the chocolate chestnut mousse.

I usually purchase medium rye flour, which has all the delicious taste of rye, without the coarse texture of a darker rye flour. I find this guide on rye flour from King Arthur to be a helpful reference.

If you can't access rye flour, you can replace it with the same amount (½ cup; 60g) of all purpose flour, so that the recipe uses a total of 2 cups (240g) all purpose flour and no rye flour.

Baking soda - Baking soda serves as the leavening agent in this cake, reacting with the acidic sour cream to create air bubbles and lift.

Smoked salt - I wanted to add a layer of smokiness to the mousse as a subtle nod to traditional fire-roasted chestnuts. Feel free to substitute an equal measure of kosher salt.

Olive oil - For this moist chocolate cake recipe with oil, I used a high quality extra virgin olive oil with a bold fruity flavor, as it pairs well with chocolate. You can certainly substitute a mild flavored olive oil, or even a more neutral oil such as grapeseed or canola oil.

Dutch process cocoa powder - This chocolate cake recipe specifically calls for Dutch process cocoa powder.

If you don't have any, you can most likely substitute with natural cocoa powder here. There is enough baking soda in this recipe that it should neutralize the added acidity from natural cocoa powder and also provide the needed leavening.

That said, since natural cocoa powder is lighter in color and flavor, you may find that the cake is not as dark in color or deeply chocolate in flavor as you'd like. My preference is to stick with the Dutch process variety for this recipe.

Coffee - I used freshly brewed, hot coffee as the liquid in the cake batter. This "blooms" the cocoa powder. Adding a hot liquid to the cocoa mixture helps dissolve the cocoa powder and release additional flavor.

If you prefer not to use coffee, hot water (or hot black tea with a smoky profile, such as lapsang souchong) will work just fine as a substitute.

Eggs - I use large eggs in my recipes. They should be at room temperature.

Sour cream - Sour cream adds flavor and moisture content. It also provides the acid needed to activate the baking soda.

For the chestnut chocolate mousse

Chestnuts - Your chestnuts should be roasted, peeled and unsweetened. You can definitely roast and peel them yourself, but I chose to use vacuum-packed chestnuts as I couldn't locate fresh chestnuts at the time.

Your options include fresh chestnuts, vacuum-packed, steamed or whole roasted jarred chestnuts or canned chestnuts. For this specific recipe, avoid sweetened chestnut spread, chestnuts ground to a paste, or chestnuts packaged in syrup.

Whole milk - The chestnuts are simmered in milk to soften them. In the process, they infuse the milk with more nutty flavor. Whole milk adds richness and helps thin the chestnuts to a creamy consistency when mixed in the blender.

Smoked salt - A subtle nod to traditional fire-roasted chestnuts. Feel free to substitute an equal measure of kosher salt.

Dark chocolate - I used a 72% dark chocolate bar, chopped finely.

Heavy whipping cream - For the mousse, use heavy whipping cream (you'll also need some for the chocolate ganache).

Do not substitute with milk, half and half, or other similar consistency non-dairy milks. They do not contain enough fat molecules to hold the air bubbles created from whipping. Using heavy whipping cream in combination with the thickened chocolate chestnut cream allows you to create an eggless mousse.

For the chocolate ganache

Dark chocolate - The ganache glaze is made with dark chocolate. I used 72% dark chocolate bar, which is on the darker end. Choose chocolate with the cocoa percentage that you'd most enjoy eating. Note that you can't substitute with milk or white chocolate as the ratio of chocolate to cream is different.

Heavy cream - For the ganache, use heavy cream (at least 36% butterfat) or whipping cream (30-36% butterfat). Higher butterfat = more stable ganache.

Do not substitute with milk, half and half, or other similar consistency non-dairy milks as they don't have the fat content required to create a stable ganache.

Frequently asked questions

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📖 Recipe