Preheat the oven to 170°C/150°C Fan (375˚F) and lightly grease three 20 cm (8 in) round cake tins, lining the bases with baking parchment. To ensure the cakes come out level, use tins that are at least 5 cm (2 in) deep.

To make the cake batter, add the coffee, butter and sugar to a large saucepan and place over a low heat; cook until the butter is fully melted and the sugar has dissolved. remove the pan from the heat and whilst hot add the cocoa and chocolate and whisk together until the chocolate is fully melted and there are no lumps of cocoa. set aside for a couple minutes to cool.

Add the eggs and vanilla to the saucepan and whisk until the mixture is smooth. In a large mixing bowl, add the flour, baking powder, bicarbonate of soda and salt and whisk to combine. Pour the chocolate mixture into the bowl and stir with the whisk, just until a smooth batter is formed; overmixing at this stage can lead to a cake that domes too much.

Divide the batter equally between the cake tins and then give each tin a firm tap on the work surface, to eliminate any small air bubbles. Bake the cakes in the preheated oven for 30–35 minutes or until the cake springs back to a light touch and is just starting to pull away from the sides of the tins. remove and cool, in the tins, on a wire rack for 10 minutes before carefully inverting the cakes onto a wire rack to cool completely.

To make the ganache, add the chocolate to a heatproof mixing bowl and melt (see below for tips). Add the sugar, cream, sour cream and salt into a saucepan. Place over a medium heat and bring to a simmer. Pour a third over the chocolate and stir to combine. Add the remaining cream in two additions, stirring well to form a silky-smooth ganache. Add the butter and stir until the ganache is completely smooth. If you have a stick blender, use this to ensure a fully emulsified ganache (see this ganache article for tips).

Set the ganache aside, at room temperature, until thick and spreadable, like the texture of buttercream.

To assemble, place the first layer of cake on a cake stand or serving plate and top with a small amount of ganache, spreading it in a thin layer that covers the entire surface of the cake. repeat with the other two cake layers. spread the remaining ganache over the top and sides of the cake, decorating as you prefer.

The cake (made with the sour cream ganache) will keep for 3–4 days, covered and at room temperature.

Notes:

Mixing the cocoa with a hot liquid, rather than mixing it with the flour, is referred to as ‘blooming’; think of it like making a tea or a coffee, the heat of the liquid develops the flavour.

The cake uses dutched cocoa powder, but to achieve a dramatic contrast between the cake and ganache I sometimes use black cocoa powder, a variety of dutched cocoa powder that results in jet-black bakes.

Tips: Using the microwave to melt chocolate

Use short bursts of heat; microwaves are powerful machines, so to prevent scorching or burning, never heat the chocolate for more than 30 seconds at a time.

If your microwave allows you to, select a lower wattage. It’s better to go a little slower than to risk scorching your chocolate.

To ensure an even melt and to prevent the chocolate overheating, make sure you give it a stir between each burst of heat, even if it doesn’t seem to have melted at first.