Chop the dark chocolate into small pieces and place it in a heatproof bowl.

In a saucepan, heat the double cream and unsalted butter over medium heat until just boiling, then pour it over the chocolate.

Allow it to sit for a few minutes to melt, then whisk in the icing sugar, cocoa powder, instant coffee, and hot water until smooth.

Let this luscious fudge icing set at room temperature overnight or in the fridge until thick.

In a large mixing bowl, whisk together the plain flour and baking soda to combine.

In a separate bowl, cream the softened butter with granulated and brown sugar for about 3 minutes until light and fluffy.

Add the eggs, buttermilk, white vinegar, and a splash of oil, mixing until smooth.

Gradually incorporate the dry ingredients, blending gently until just combined for a rich batter.

Preheat your oven to 350°F (175°C) and grease three 8-inch round cake pans.

Carefully divide the prepared batter evenly among the pans, smoothing the tops with a spatula.

Bake for 25–30 minutes, or until a toothpick inserted into the center of each cake comes out clean.

Allow the cakes to cool completely on a wire rack before assembling.

Once your cake layers are completely cool, level the tops if needed to ensure a flat surface.

Place one layer on your serving plate and generously spread a layer of the fudge icing on top.

Add the second layer and repeat, topping it with more icing.

Place the third layer on top and cover the entire cake with a smooth layer of icing.