11 January 2019

CHOCOLATE WALNUT COFFEE CAKE

Now that the winter is in full swing, the time is right to bring out the true winter classics – rich chocolate cakes full of nuts and spices. For me, the combination of chocolate and walnuts has always been a wintery dessert combination. Warm flavours pair wonderfully with chocolate and coffee, and just a dash of cinnamon, to accentuate the signature winter spices.
Even though chocolate cakes are traditionally seen as heavy or overly rich, with dense buttercream fillings, this cake is quite the opposite – the coffee mousse filling is marvellously light and airy, yet robust, with lots of white chocolate specks in a gorgeous stracciatella style. The whole cake is so soft and tender, making it a perfect addition to afternoon tea, or a wholesome after-supper treat.


Ingredients
For the chocolate cake layers
250 grams plain flour
20 grams unsweetened cocoa powder
200 grams granulated sugar
1 ½ teaspoon baking soda
½ teaspoon salt
¼ teaspoon ground cinnamon
350 ml water
120 ml vegetable oil
1 teaspoon espresso powder
2 teaspoons vanilla
1 ½ teaspoon apple cider vinegar
100 grams dark chocolate callets
100 grams walnuts, chopped
For the coffee filling
800 ml whole milk
150 grams granulated sugar
5 teaspoons espresso powder
80 grams cornflour
30 grams unsweetened cocoa powder
2 egg yolks
250 grams unsalted butter, room temperature
200 grams real white chocolate
For the decoration
200 ml double cream
1 tablespoons unsweetened cocoa powder
100 grams dark chocolate

Preparation
To make the cake filling, take a large bowl, and sift in the cornflour and the cocoa powder. Briefly whisk them, then add in half of the sugar, as well as the yolks, and blend really well. Finally, pour in 200 ml of milk, and blend everything together. Pour the rest of the milk into a heavy-bottomed saucepan, add in the rest of the sugar, and the coffee, and place it over medium high heat, so the milk can come up to a boil slowly. Once it starts boiling, add in the cornflour mixture in a thin stream, and cook, while whisking constantly, until it thickens up, and becomes a very rich, fragrant custard, about 2 minutes. Remove it from the heat and strain it through a mesh strainer, then cover the top with cling film, and let it cool down to room temperature.
While the filling is cooling down, make the cake layers. Take a large mixing bowl, and sift in the plain flour and the cocoa powder. Give them a quick whisk to blend, then tip in the granulated sugar, salt, cinnamon, and baking soda, and whisk again. In a separate bowl, mix together the water, oil, espresso powder, vanilla, and vinegar. Add callets and the walnut pieces to the dry ingredients, and mix well, then pour over the wet ingredients, and mix until combined. Do not overmix, because the cake will be tough. Pour into four lined round cake tins (15 cm), and bake them immediately, in a preheated oven, at 180°C (350°F), for 20-25 minutes, or until they spring back when lightly touched. Let the cakes cool in the pans for about 10 minutes, then take them out, and let them cool completely on wire racks.
Once the custard is at room temperature, place the soft butter into a large bowl, and beat with an electric mixer on high, until it becomes very light and creamy, and resembles buttercream, about 3-4 minutes. Take the bowl with the prepared custard, and mix it briefly with the mixer so it becomes smooth and creamy. Continue mixing the custard, while adding the beaten butter, a tablespoon at a time, until all of the butter is used, and the filling is smooth and lush.
Place the filling into the refrigerator while you melt the white chocolate. Melt it slowly, over very low heat, or in the microwave, making sure every last bit of it is melted. Let it cool down sufficiently so it doesn't melt the filling, yet is still pourable. When the chocolate is ready, take the filling out of the refrigerator, turn the mixer on the highest setting you have, and without stopping the mixing, pour in the melted chocolate in a very thin stream. This will create the stracciatella effect in the filling.
When it is ready, level the cake layers if needed, and place the first one onto the serving platter. Evenly spread one third of the filling on the first layer, and top it with the second one. Continue stacking the layers until all of the filling is used. If your kitchen is very warm, you might need to place the cake in the freezer for a little while between stacking, so it firms up, as the filling is very light and airy.
Place the assembled cake in the refrigerator for at least 4 hours. When the cake is firm enough to decorate, whip the double cream with the sifted cocoa powder until stiff peaks form. Melt the dark chocolate using your preferred method, and let it cool down so it doesn't melt the cream. Generously cover the whole cake with the whipped cream, then drizzle with the melted chocolate. Place it back into the refrigerator until serving time. Yields 16-20 servings.

Baker's note: As with any cake, you can place it into the freezer for a bit before serving, so the filling takes on an ice-cream texture, or you can serve it with a lush chocolate sauce, such a chocolate-whisky sauce for example.

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